I figured it out! I haven't written it yet, but I know how my current book will end.
*big sigh of relief*
I've had some ideas, but my original plan hasn't felt right. Initially I wanted my main character to die, but I keep hearing how readers don't like that and my stubborn side wanted to kill him for that reason. But it got me thinking that maybe he should survive. He can almost die, but then I'm facing the generic "hero almost dies but makes it at the end, possibly waking up in a brightly lit hospital room surrounded by loved ones." I do NOT want to write that kind of book.
Yesterday I didn't do any actual writing, but I did take a page worth of notes and I figured it all out. My ending will wrap up a lose end without turning it into a cliché, and someone will still die.