There really doesn't seem to be any way that Cain can get Misha back without becoming powerful enough to go to that other world and get her. But just as importantly, the feminine voice said that disaster was coming for this world, and the world itself was unlikely to survive at its current power level.
Cain isn't sure what that means, but there are a lot of possibilities, given the little bit that he knows about this world's history, and none of them are at all good for him. Especially if it's the human Gods or someone else at that sort of level that is returning. The ley line device in the Ancient City said that the planet is currently below ten percent of what it took the Ancients to even fight to a stalemate last time before those who could flee did, and the rest were annihilated.