I’d need a lot more description of the whole situation, and the game, and if there are one or more “opponents” in the game, who they are. And who is offering a billion dollars and what other conditions and circumstances are involved, and whether I trust them or anyone else who might be involved in the situation. I’d tend to suspect it was not a fair and no-strings attached where anyone was really offering me even a 50% fair chance at a billion dollars with no strings attached and that “winning” wouldn’t put me in a dangerous situation too.
If I were certain it were a pure 5/6 chance of receiving a billion dollars with no negative consequences except the 1/6 chance of dying, then I would probably accept. But the odds seem very low that would ever actually be the case.