I think he'd have to be. After all, Cain lived for millennia with the Mark. He also has some of the can't-be-killed sense of immortality, because if he is killed he comes back as a demon.
I haven't seen seasons 10 或者 11 yet, but my guess would be either a special weapon 或者 spell, 或者 Cain isn't really dead. 或者 are 你 talking about Dean at the end of season 9? He wasn't fully immortal in the sense of being impossible to kill, but he could easily return as a demon, as we saw.
