I read an article in which the novelist, Kristopher Jansma, explored the issue of finding the proper ending for a novel. He was plagued by the question of leaving the ending ambiguous, or of tying things up in a neat knot—one that would leave the reader “satisfied.”
The article referenced Aristotle, and Rowling, and quoted Chekhov and Vonnegut, saying among other things, “a novel aims not to represent just a slice of life, but the whole of it. We need more than just artfully posed questions. We expect to know unambiguously who is virtuous and who is corrupt, and have a novelist mete out fates accordingly.”
The author commented on the occasional need for an ambiguous ending to a novel, quoting from The Gotham Writer’s Guide.