The Ending is arguably the most important scene in a film/story. It is when the filmmaker/writer/creator states what it is they are really saying – it is when they prove their Premise/Controlling Idea/Main Theme. The ending can lift a mediocre film into the stratosphere or delegate what was great entertainment onto the heap of mediocrity.
I say arguably (it is the most important scene!) because without all those preceding scenes you would never make it to the end. But the ending is where you are left satisfied, or you walk away with a bitter taste in your mouth.
So, the ending and the premise is inextricable linked. And it is in the ending that the premise is proven. During design of your story, once you know one, it suggests the other.
*Note: Sometimes the ending and the denouncement is one and the same… but I believe the denouncement is best served ‘after’ the ending. It is like seasoning a meal just before you lay it in front of the guest – giving it an edge, a spice!