Writing With the End in Mind... or Not

In several previous posts, I've mentioned my "vomit" draft -- a draft so jumbled and stream-of-conscious that it doesn't deserved to be called a first draft. Today, I reached the point where I think there's just one chapter to go, after which I'll be able to start writing a real first draft.

But I'm having trouble pulling the trigger. I'm not  sure I want to write this last chapter. I'm not at all certain I want to know, just yet, how the story will end.

I had no idea how Bill Warrington's Last Chance was going to end until the very... (my editor will not like the repeat here) end. I wonder if that was part of the fun in writing it, and part of the motivation to keep going with it.

Yes, yes, I know that the ending will likely change--most likely with each future draft. And yet... not finishing this chapter seems disloyal to the vomit draft, which has waited patiently for me to get to this point since last October. It has put up with my blogging, my Facebooking, my Internet surfing, my sudden need to clean the desk and straighten the shelves while it remains open on the screen, waiting.

So do I bring this vomit draft to its conclusion, offer it a sort of closure, or do I leave the ending for the first official draft?

Some writers know exactly how their stories will end before they begin writing. What's your approach? Do you already know the ending while you're writing that first/vomit draft?