It's the end of the world as we know it, and I feel fine:
Endings in Fiction
By Theryn Fleming (Beaver)
"A novel is like a symphony in that its closing movement echoes and resounds with all that has gone before. … It is this closing orchestration that the novel exists for. If such a close does not come, for whatever theoretically good reason, we shut the book with feelings of dissatisfaction, as if cheated." John Gardner in The Art of Fiction.
If a story has worked, readers will have been drawn into the world created for the characters; they will have fully invested in that world. Because they have made this commitment, when they reach the last chapter, page, or paragraph, they will expect an ending that is clear, satisfying, and delivers on what the story promised.
If an ending is successful, readers should be left with a feeling of closure. This means that the central conflict and any subplots have been addressed. It doesn't mean that every loose end has been tied up in a bow; nor does it mean that the ending has to be happy or be the one readers hoped for. However, if an author leaves a substory unfinished, perhaps to indicate how life goes on, or to set up a sequel, it should be clear that this was an intentional act. If a plot point is introduced and just left hanging, readers will believe the author has forgotten it. Readers should not be left perplexed about what happened to Great Aunt Harriet after they last saw her going to the store on page 172.
There should also be a sense of inevitability about the ending. In other words, readers should feel like this ending is the right ending for this story. Understand that knowing that the ending is the definitive one for the story is different than liking how things turned out on an emotional level. Readers can know that the author made the right choices for the story even as they are sobbing their guts out because the protagonist has met his demise. What shouldn't happen, however, is that readers immediately start writing alternate endings in their heads because they just know they could have done it better.
Finally, readers should feel that what has transpired has some significance. Readers don't want to feel like they've wasted their time on something completely trivial. One way an ending can disappoint is when it's obvious. With few exceptions, readers shouldn't be able to predict the outcome from the opening line—a great deal of the fun of reading fiction comes from not knowing how the story is going to turn out. Another disappointment is the non sequitur—the ending that appears tacked on, because the author either didn't know how to end the story, or, for whatever reason, just wanted to wrap things up. For example, a serial killer is squashed by a falling piano, whereupon the murders stop, and the detectives in charge of the case quickly put two and two together.
How to end a story depends on both story length and genre. Some kinds of endings are appropriate for short stories, but not for novels, and vice versa: a twist ending to a novel will probably leave readers feeling ripped off, while an epilogue would be superfluous to a short story. Similarly, some endings are more suited to certain genres than others (see below).
When to end a story is almost as important as how. A story should not go on too long after either the central conflict has been resolved or it has become clear that no resolution is possible or readers will become bored and the ultimate ending will be a letdown.
Here are some ways to end a story. Note that the types aren't mutually exclusive, and that in a longer story or novel the ending will probably be a combination of the types.
With ideas from: "Is it really over?" by Rita Marie Keller, "How to Write Successful Endings" by Nancy Kress, and "Writing: Plot" by Damon Knight.