It’s as important to know when to end a story as it is to known where to begin it. Sometimes there are important ramifications that don’t show up in “story time” for a considerable length of time, such as years or even generations. However, it presents the final closure that makes it complete.
One way to wrap things up is with an epilogue. They well to cover “the rest of the story”, i.e, that which relates to the plot, but occurs a long time after the story officially ends. They can even involve minor characters, or in some cases, someone who wasn’t in the story at all.
Of course if you think you have enough story material to fill the gap, then you may have a potential series on your hands. Otherwise, epilogues offer an easy way out to tie up any loose ends.