Naturally that logic only works if the possibility of a god existing happens to be the one god you pick to worship. Problem is, if a god existed it could well be one of the thousands and thousands of gods man has worshipped for time immemorial… or even another god that man’s mind has yet to conceive. Thus, if one picks a specific god to worship, the odds of THAT GOD being THE GOD, the CORRECT GOD, is from a mathematical perspective, rather small…infinitely tiny.
So as oppose to having nothing to lose, a Christian may well find themselves confronting a god who is pissed as hell that his creation has been worshipping the wrong god and giving the wrong god all the credit his whole life. Homer Simpson figured it out when he said: “But Marge, suppose we've chosen the wrong god. Every time we go to church we're just making him madder and madder."
In fact, there’s a good possibility (better than even odds I say) that said god being would be more sympathetic toward an atheist who worshipped no god because there was no supporting evidence for any. If nothing else, atheism demonstrates the admirable quality of reason and logic that, presumably, this being would have wanted man to demonstrate…seeing as how this god would have provided those attributes to man in the first place.
Believe in God because you’ve got “nothing to lose and everything to gain”?? Yeah…nothing to lose except your ability to reason and logic; your grasp on reality; a loss of self sufficiency; and conducting your life encumbered by inane dogma and superstitious fears.