I've always suspected Eleven to be one of the characters killed off in the final season, so her death would not be a shock (no matter how it happens). I'm hoping Lucas is not killed off (and playing into one of film fantasy's worst tropes), as it would be terrible for Max to be restored, only for Lucas to end up dead.
Hopper has been teased as dead before, so one would imagine the showrunners would not take the character in that direction again.
Jonathan has been sort of "just there" of late, and that's just the kind of character who would be written to step up to have some final, unexpected big moment, so I believe he's high on the Grim Reaper's list.