Ideally I'd like to have a look at the story to determine the labels, but from your description, I'd say AU - I wouldn't label it futurefic as it's not set in any canonical version of the Supernatural future universe, really - and I wouldn't warn for character death if the character comes back as any sort of vampire/zombie/undead; I'd only warn for character death if they're basically worm food, still and corpsey.

But these are just thoughts :)