What I’m trying to say is the first four chapters are about four different people by themselves, then they’re together the rest of the book and all die except one, but that one is very important and it’s supposed to be realized that he was the definite main one throughout the whole series. If that sounds confusing here’s a the simplified question: Is it “too much” for the reader to get attached to all four characters then just just follow one after the first book, especially if he wasn’t the most likable one?
There are more things to consider, with regards to who is the main character, than who is "the most important to the plot". Who is the POV character(s)? Whose inner thoughts do we hear? Whose emotions do we follow? (The POV character is not necessarily the MC - Sherlock Holmes is a famous example to the contrary - but it is one element that would affect how your readers view the characters.)
If all four characters get about equal POV time, you can compare your story to Song of Ice and Fire: readers certainly get attached to G.R.R. Martin's numerous POV characters, and those POV characters certainly die partway through the story.
You mention that your four characters are together for most of the book. In that case you need to consider group dynamics. The leader of the group is not necessarily the MC - The Lord of the Rings is a contrary example, but if you have one POV who is the leader, and three POVs who are tagging along, the character who's most active in making decisions is going to feel like the MC.
And one last thing for you to consider: you are worried about definitions. Is there any particular reason why you can't have four MCs? Or why a character who is not really the MC of the first book of your series can't grow into the role after his companions die? Those are just different ways to look at the setup you presented.
It sounds to me like you have Book 1 with four main characters, and Book 2 with only one of those characters continuing. Lots of series do this, including Narnia and Dragonlance.
But, it's important that Book 1 work in its own right. You don't want to get rid of major characters abruptly just because they're not going to be in the next book...
You absolutely can kill off main characters; please don't treat a character who dies as "less important" than one who lives. If/when you kill off a main character, you want their death to feel like it's got narrative significance -- e.g. an inevitable tragedy, or a sacrifice to accomplish something, or falling victim to a horrible enemy... you have many many options, but build up to it, make it mean something, because that character's life and death is its own plot-arc in your story.
As We Write, We Learn
There is a well-known quote by an author E. M. Forster:
“How do I know what I think until I see what I say?”
Freedom of Creation
Allow yourself this first act of freedom to create your draft as you see fit. Silence the inner critic simply by telling your Inner-Critic,
"Wait until after, then we can determine how "good" it is. For now, let's just get the words down, no matter how "bad" so we can see the the artistry of the story I am attempting to tell. Then, if you (Inner-Critic) are right, we can determine how to change it or leave it behind."
There is the additional possibility that your Inner-Critic is correct. It could be why you are led to ask this question about whether or not readers will be disappointed. Could it be that your own subconscious is trying to send you a message that the story won't work this way? But determining that is for later. For now, get the story out.
Think Of Yourself As a Consumer (Reader) of Your Story Too
Take just a half a step back and consider your own story. Do you like the way you are telling the story? Do you like the effect of all the other characters dying and only the one living thru to the end?
Art And Style (Voice In Writing)
Keep in mind that you are the artist and it is ultimately up to you. You could be on the verge of creating an entirely new POV (Point of View) concept.
Check out House of Leaves by Mark Z. Danielewski. That is a very new and odd concept, but he did not ask someone else what they thought.
If you think this story method works best then write it. Write it better than anyone else because only you can. It is your format.
Get 100 People to Read It
After you write a complete draft get 100 people to read it. Do you believe you could convince people to read it for free? Then you believe in your story and you should (no, must) write it in your format. If you do not believe in it...run from it quickly.
These small decisions do not really matter. What really matters is that you write it the best you can and that you believe in it so much that you would read it aloud to strangers because you know they will love it.
I'd say no, if they are well written you can get readers attached to many characters and as long as a main character is compelling and relatable they don't have to be particularly likable at all to be satisfying as a main protagonist. David Gemmell's Druss is, for example, a real nasty piece of work a lot of the time but because he has his, obvious, reasons for being that way he's still a good leading character.
A quick note, people don't always see what we want them to see and they don't always miss what we want them not to see. You will have readers who realise what you're doing and where the narrative is going long before you get there this may put people off or it may cause them to get greater enjoyment from the narrative, you don't know until it happens.
My advice in situations like this is always the same, it's the same advice I've gotten from a couple of my favourite authors over the years, "write yourself the story you want to write, the way you want to write it". If it's good enough to get the attention of a publisher you can fight over final styling and other compromises when that time comes.
Yes, it will be disappointing, but that disappointment will not likely occur at the end, but much earlier when the reader begins to get the sense that the character they are following has no arc. Once they realize that, they will stop reading and never reach the end.
A story is not a history. A history can have multiple players who come and go as much by chance as by design. Story is precisely a rejection of the randomness and purposelessness that history presents to us. (So much of history, and news, is falsified precisely to give it the shape of story that it does not have by nature.)
A story is about one person (though a novel may weave together several stories). It follows that person through some disruption in their life (which may come from within or without, may come through desire or loss) which leads to a moment of decision in which they must face up to who they are and what they are willing to do. This decision may be faced on the battlefield or in the drawing room, before the mast of a storm-tossed ship, or in the heart of an uncertain lover, but it is always there, and it is the pivot on which the story turns.
What draws the reader on is the sense that this character is likely to have to face such a decision, and a desire to see them face it. The sense of the coming crisis may be faint at first, but it must grow stronger as the story progresses. The tension around the character must increase as they are led towards the point where the decision must be made. It may build quietly or it may build loudly, but it must build.
But none of this can happen if we don't know who the main character is. The main character is, by definition, the one whose life is leading them towards such a moment. The reader is looking for that person, and either they will find them and continue, or they will not find them and will abandon the work.
If you provide no identifiable main character, they will be disappointed early and bail early. If you provide a false main character, whose life seems to be heading towards this moment of decision, but isn't, then the disappointment will come as soon as the reader recognizes that they are on a false trail, and then they will bail.
If you do it well, it can make for a thrilling ride, especially if it seems like one character is the main but then they die, leaving you to wonder who is the real lead. If you keep killing off people, or having them leave in other ways, the reader is always going to be guessing and that makes for an exciting read as you can't wait to finish. Killing off lots of popular characters annoys some people (or so they say), but if it's relevant to future sub plots later, they can be an important part of the story.
Just look at the ice and fire books, after book one, do you have any idea who the primary characters is in the entire story?
Even after book five, (and the tv shows that went further), we still don't know if there is even is a primary character, or if it's maybe a group of characters, or none (as it's a tale about the [history of the] world, and may not be not following a single characters journey at all.
At best, we only really know who has lasted the longest up to this point. We know more deaths are coming so it's quite possible the entire series was the story of one character with fillers elsewhere to build to the story of the world and the other sub characters throughout. It could be one family that triumphs and is the primary object, or it could be that "man" triumphs over the Smurfs with their shiny new dragon. It could quite literally be anything, and the storytelling has been done quite well so that we just don't know until the final page of the final book (or final show if it is going to be one story, target than told two ways; a book ending, and a series ending).
As someone who is more of a consumer than a creator of writing (in the sense of storytelling), I'd like to offer an example of a piece of media that did just that.
I'd like to preface that this answer contains some spoilers!
In the video game Metal Gear Solid 2, the game revolves around the character Solid Snake, the definitive main character of the series. He is an unstoppable hero with incredible cleverness, near superhuman abilities, and more or less a "power fantasy" character. When the game was coming out, of course, everyone was excited to return to the life of Snake and his story.
However, in Metal Gear Solid 2, you only play as Snake for a very short time before you end up playing as a different character who, in short, does not encapsulate many of these qualities; in fact, he is more or less a wimp! Although the rest of the game is told through his eyes, it is revealed that all major story points actually revolve around Snake and his actions that are occurring in the same setting. You, the main character, often tend to just get in the way or cause more problems that he cleans up, but at the end of the game it is all revealed that he was the real protagonist as far as the story is concerned.
Of course, not many people who played the game came out feeling cheated; many consider it to be an amazing example of post-modernity in the video game industry. This is because playing through the eyes of the second character did not hamper the story; it gave a fresh viewpoint to experience the story, and it gave the player/consumer agency.
Now, obviously, a novel has different ways to achieve this, but I think they both revolve around the same idea: character viewpoints other than the main character are possible, and when done well, exceptional! One just needs to make the narrative beyond that character engaging, and make the consumer care about the other character enough to establish agency and immersion.
In short, it won't necessarily be disappointing to tell the story through the eyes of non-protagonist characters, but it will be challenging to build a narrative strong enough that it persists through the actions of the protagonist and establishes a connection with the reader through the supporting characters.
YES it will be disappointing.
+1 Mark, I think the same; a story is about a main character.
I would add this: Introduce his POV first, he will be assumed to be the MC. Then yes, you can let his sidekicks die, even if they are "leaders". Keep his POV the most intimate, that is another signal of MC, the one that thinks most of love and family, his responsibilities to others, their fate if he dies, his emotional goals. Don't go quite as deep on the doomed characters in their POV, e.g. keep their love interest rather light, for the reader's benefit they can be admired, and even better than the MC in most respects, but you want the reader to intuit these characters have a bit less to lose, their lives are simpler and their deaths won't be quite as devastating.
I would prefer the MC be the only POV, but that can restrict the plots you can write. Mark is correct, I think you must constantly nudge the reader into seeing the lone survivor as the MC.
Look at Tolkien; Frodo is the MC (it seems) in Lord of the Rings; but we have other characters that are far more powerful: Gandalf, Aragorn, Legolas. Your MC does not have to be the most fascinating of your characters. Often, the other super-competent characters DO die protecting the chosen one, or choose their death because they are the only one that can accomplish some key element of the mission, and accepting their own death as the price is their contribution to the ultimate success.
Edit for OP comment:
But there is no POV it’s all of them as a group.
In that case, broaden POV to mean whomever the narrator seems to be focused on primarily; and your first POV is the first character in Chapter 1. The reader will assume that is your MC, unless (like in Harry Potter) that and other characters are strongly focused on an off-screen character (Harry Potter). Characters focusing on serving another character (even an infant like HP) is a tool to imbue the other with great importance (for another example, consider a show that opens on thugs and cops, the cops want to know where Big Mike is, the thugs are clearly fearful of Big Mike and take a beating without telling the cops anything --- Clearly Big Mike is the focus of this first scene, and very important, even though the audience has no idea who Big Mike is at all).
Even if the narrator cannot get into the thoughts of the characters, we (readers) should still feel like the MC is our main guy. You could make them more expressive, and give them more dialogue, follow them more closely when the group is together.
This story does have a main character, the survivor. Obviously this is all my opinion, as is every other answer, but you just can't have an MC that dies with chapters left in the book, that is too much of a break with the laws of (modern) fiction. That is what will happen if you allow the audience to think somebody else is the main character, and that character dies. In your tale, the 3/4 of readers that mistakenly focus on a non-survivor as their MC will be disappointed when that char dies, and not in a good way, in a "stop reading" way, because when their hero dies they are done, they no longer worry about what happens to him, they know! He's dead!
That was your question, nobody should reassure you otherwise; the modern audience for fiction has expectations and this would violate them, not in a good way. I doubt it would be taken up by agents or publishers, and if you self-publish, you may sell a few copies but those readers won't recommend it, and may publicly denigrate it as poorly written.
Your MC does not have to be the most powerful; we understand heroes (the other three) dying to protect something important to them. In Star Wars, Obi Wan sacrifices himself to save Luke, Gandalf dies fighting the Balrog to save Frodo, Dumbledore dies in Harry Potter and the Half Blood Prince. We often see powerful mentors or characters fight and die to protect weaker main characters, or the group, or to prevent failure of their mission.
If your MC is the most powerful, the other deaths can humanize him, as failures: He failed to protect them, misjudged their opposition, and so on. He can feel guilt and failure in losing friends, even if he is victorious in all his own battles.
I have read a lot of wild books which broke with any and all conventions about anything story-related at all. (Seeming) main characters dying were some of the most memorable moments, and not only since Song of Ice and Fire.
Go for it. Other aspects will make or break your story. The number or overall fate of your characters will not decide anything (obviously, as long as you can present your book in a fashion that does not leave the reader completely behind).
The original Star Wars did this very well. It was only in the last minutes of the film did we realize that R2-D2 was the main character.
Keep your main character in most scenes, but don't focus on him in most scenes. Your readers will thus build up empathy for him just as they did for R2-D2. As your concern is to not have the reader become disappointed, you could borrow another tip from A New Hope: have the character become injured near the end, then let the reader feel relieved at him being spared.