-Some mythical/ magical object that their life then becomes bound to.
-A sacrifice of equal/ similar value.
-Partially restoring them to life. Eg. necromancy, zombies, vampires, "downloading" their consciousness into another form.
-Using sci-fi medicine/ technology.
-Fate/ a deity intervening because some higher purpose is not yet fulfilled.
-Reincarnation with past life regression.
But whatever way you do it, make sure the risks/ drawbacks are very high, otherwise death is about as meaningful as getting a splinter. Unless that's what you're going for, of course.