As far as Christianity is concerned, it seems somewhat pointless to speculate on this: the Book of the Revelation says that the Devil will be thrown into the Lake of Fire, which doesn't sound like such a peace will ever be made.
I hear that when God made the devil, the devil was God's favorite angel. He loved him so much that he gave the Devil so much power. So much power that the devil thought he could rule the universe....
Well it is dependant on what religion the person personal opinion, how many gods you are talking about. Because Gods' is referring to multiple Gods and God's is referring to one God.