grose, that's a dumbed-down version of Pascal's wager with more holes in it than an old bucket.
(1) When there are two alternatives the probabilities don't have to be fifty-fifty. Like: During the next year, there will either be a war between Canada and the USA or there won't. Therefore, there is a 50% probability of a war. Silly.
(2) There are many religions and sects, so if you follow the rules of one sect or religion, chances are that the real God may tell you after your death that you should have followed the rules of the....to gain eternal life.
(3) Many religions portray their God as benign. There are chances that a benign God may accept all good people near him whether they have followed a specific set of rules or not. (I grin to myself as I picture an orthodox Jew debating with God after his death why all those non-Kosher eaters have been admitted to heaven as well and God telling him that he didn't actually care about the rules but about leading a good life)
(4) An omniscient God would know if the rules are only obeyed with an eye to the afterlife and therefore would punish those who have followed the rules for that reason alone.

These are just some of the many arguments against Pascal's wager.

Wolfgang