This could end very well or not, depending on how you write this.
The way you leave the reader satisfied is simply how your write. I know that you want more structural and helpful advice, but that's really it. If you can write well enough to leave the reader thinking that Darius died an honorable death, you're going to have to comb through your story multiple times to make it the best you can.
If you want your character to die an honorable death, you need to show how the character either gives himself up in the name of something greater (which I think is your plan, since he's a POW) or have him not "plan" to die, but die in a finite way. making it honorable is hard to do, so I would look to something like Harry Potter (bad example, but it's the first that came to mind) and look at people like Fred, Lupin, Sirius, and Harry's parents. These people all died honorably, and that can give you a starting point if you can figure out what they all have in common (hint: they all care about someone).
As for the other two characters getting on with their life, I think that's a good idea, but you have to remember that everyone handles death differently, even characters. Let your characters feel sad for a period of time, then show them slowly realizing they have to move on and still live life.
I hope this helps :).