Nine times out of ten, I don't have a clear ending. Maybe that's why I'm so scatter-brained. lol I will though have a vague idea of what should happen. Like, in a romance, for instance, they either end up together or they don't. You pick one and move toward it.
The story I've been working on for a while now is PBox, and when I started it, I did have a very vague idea of what would happen in the end, and that's what will be the fiftieth chapter. Everything up to that point, I had yet to think of. I think it was around chapter nineteen when I figured out how I wanted the story to end. Nick and I had an argument about it, and the two of us settled on an ending that made both of us happy. lol
So I'd say just have a nice little chat with your characters and decide from there. lol