Some novelists struggle most with the ends of their books, writing multiple drafts—all of which turn out just as crappy as the first. The good news is that the Bests have this same problem. The bad news is that you’ll never finish your book unless you stop trying to make it perfect.
All your creative writing teachers—not to mention your impossible-to-please critique group—have told you once if not a hundred times that you need to tie up those loose ends. And while, for the most part, they’re right, if your readers stick with you till the end, you better give ‘em some answers!
BUT, don’t worry about delivering absolute resolution. If you want readers to be thinking about your message after the last page, then you have to leave them with something to wonder at. Happily Ever After is nice for Disney, but it’s the death of your characters. Readers can easily shelve your novel, and walk away with the empty satisfaction of seeing something to its end.
I’m not saying happy endings can’t be brilliant ends, but Happily Ever After can't. It says “the most important part of my characters’ lives are over and they will do nothing else challenging for the rest of their lives, but they’re happy forever, so it’s okay”. No. That is not okay.
If your book is to have any lasting impact, those loose ends have to be tied with room to slip. Perhaps the bad guy still has too many followers; perhaps the protagonist’s brother died, leaving emotional struggles for him to work through; perhaps they’re still not over what happened in the book but they’re moving on to the best of their ability.
In all of these scenarios, the end of the book is more like the end of a chapter in the protagonist’s life. But what if you don’t want to write a sequel? Okay, don’t. Really, it’s not necessary as long as you've written and ended your story in a way that leaves the reader feeling confident in the protagonist’s ability to handle that future.
Readers want to know that your characters have conquered what they set out to conquer, and that they will be able to take on whatever may come beyond the back cover.