+1 Shadocat; I will expand on that answer with reasons.
Epilogues are especially welcome if your story is strongly focused on characters, and throughout the story they (like most of us) have thoughts about their future, plans and fears.
If your story centers around an issue in their present life, it may only cover the span of a few months. But in the course of that few months, the reader may come to feel they know your primary characters like friends and family.
Technically, the story is over when they finish their mission. But this can seem like too sudden an ending, and unsatisfying to the reader, like suddenly walking away forever from their friends and family. All the dialogue and feelings about their future feel like loose ends! Even if the main problem is solved, it doesn't feel to the reader like the character stories, or arcs, are completed.
You can tie up those loose ends in an epilogue, whether or not the main crew will return for another story. Epilogues are generally conflict free; NOT a story, just the reporting of the facts to tie up loose ends, the personal issues your characters (and readers) were worried about.