Quote Originally Posted by The Crystal who is endlessly posting SOS's theory for us
(Zeromus' final words.)
Zeromus: I will not...perish...so long as evil...dwells in the hearts...of
mankind. G...gh... GRRRAAGH!
It is never actually disproven that Zeromus is immortal considering after the party beat him the game ends so I don't class this as valid evidence. I could also say the exact same about Necron.