In my campaign, character death happens when a player ignores “are you sure?”. Everyone’s been informed of this ahead of time, and they get a reminder at the critical moment as well. There’s always a way out, it’s just that oftentimes the way out isn’t what that character would do. And then they die. Everyone’s been very happy with this system.

The vainglorious paladin won’t back down against an enemy they are very clearly failing to handle? That’s a character death. The player knew and accepted it. She didn’t want her character to die, but she couldn’t see a way to justify him running away like the characters who survived did. Now she has a slightly less brave character.