I thought this would be a fun discussion. Most Goosebumps characters survive their book's evil. There are a few who have died or whose lives have been drastically altered by the events of their book. Let's list/discuss those characters here!
Be mindful of spoilers if you haven't read all of the books and don't want to be spoiled. I tried to find a spoiler tag, but I'm not sure we have one, so it might be a good idea for people to bold titles in paragraphs they are discussing a character so visitors can skip paragraphs of books they worry about spoiling.
Anyway, I'll start us off!
In The Barking Ghost, Cooper and Fergie accidentally switch bodies with chipmunks and presumably live out the rest of their days as rodents. That's awful.
In How I Got My Shrunken Head, Dr. Hawlings, Carolyn, and Kareen are shrunk to the size of mice by Mark's Jungle Magic, and run off into the woods. R. L. Stine stated in an interview that he doesn't know what became of Dr. H, Carolyn, and Kareen. They probably were eaten by a jungle predator.
In The Horror At Camp Jellyjam, at least three kids are eaten by King Jellyjam. This has got to be the worst outcome of a book's evil. They were never named, though.