Possible Worlds and God

OK, so it is beyond the level of logic I know how to work with, but supposedly Alvin Plantinga has a reworking of the ontological argument for the existence of God that uses what is known as “S5” modal logic. While I don't know how to do S5, I think I understand the basic principle, which is that given an infinite number of possible worlds with all possible combinations of states existing, God must be necessary in at least one of them. And if a necessary being exists in one world, He must exist in all worlds.

The interesting thing that strikes me (though I don't know if it would work) is that it seems like the opposite must also be true: there must be at least one possible world where God does not exist (according to Plantinga's initial premise). Thus, we would end up with one possible world in which God must necessarily exist and not exist simultaneously.

There's a mind boggling thought. I tend to think using possible worlds to theorize is only questionable useful, but it is interesting.