Here are a couple of questions asked by a new apostate:
Can I continue believing in God after I leave Islam?
Absolutely! There is no reason to give up the belief in God once you discover that Muhammad was a charlatan. This is like a follower of David Koresh or Warren Jeffs decides to disbelieve in God after realizing that his false prophet was a liar. What those conmen had to do with God? Muhammad had nothing to do with God either. Yes, it is perfectly okay to believe in God after you leave Islam.