First of all, we're judging this fictional character according to his modern description as
omnipotent. (As opposed to the mountain-dwelling spirit of the early Old Testament.) Can an omnipotent being kill itself?
Shortest answer: no.
Medium answer: Omnipotence does not imply transcendence of identity. You can beat God at
tic-tac-toe if you start as X and know what you're doing! He could smite you for this insult, but he'd still have lost. God can only do things that are natural for God. He might be able to
su into to other identities, but he cannot disable the
root account or scramble the password to lock himself out. And he can always reinstall the OS or get a new computer if he wanted to.
Longer answer: see the Wikipedia article on the "
omnipotence paradox".