vivec was a mortal over 200 years before skyrim, remember? there's no freaking way he'd live that long.
The Nerevarine is a different story, but then again you play as the nerevarine, so that's nor going to happen ever in skyrim
well i think he was a mortal ELF over 200 years before skyrim
so thats not that long for them i dont think
but to the OP
it was never said he was freed from the deadra, or that they didnt kill him
so i doubt he will make an appearance or even be mentioned
pretty sure that was beths way of getting rid of him