I'm very close to the end. I have one conversation and then it's the epic final battle, the bad guy loses, the good guys (mostly) win, and then there's the nice little denoument to wrap up everything into a tidy ending.
The thing is, I just today realized what it's going to take to turn the C-plot into a fully-realized, story-strengthening B-plot. I need to add in hints, foreshadowings, a couple of mysterious events that shouldn't be more than a couple of paragraphs, and finally write in one big scene containing a kidnapping, a battle, an unexpected alliance, a rescue, and an armed truce.
Since I'm a dyed-in-the-wool pantser, there's a very good chance that what happens in that big scene will change the ending. Not drastically, but it might change the specifics of what goes down, how it goes down, and how the 1st person viewpoint character reacts to it.
So should I finish, then edit and chance that the ending will have to be completely rewritten to accomodate the new scene? Or should I go back and write in the new scene, then pick up where I've left off and write through to the end? Any advice?