In the comments someone says:
>Except that, even if the gun never fires, you would die of old age. It doesn’t stop physics and biology just because the gun doesn’t fire.<
…but that doesn’t seem to necessarily be the case. In one of the non-dead worlds that “splits off” (whatever that means) you might end up as a brain in a jar or suchlike, able to wait for technology to advance until such time as you can be uploaded to an artifical consciousness machine (whatever that means).
An obvious question is: would that still be “you”? But if the many-worlds interpretation is correct, “you” have always been this infinitely composite entity, so presumably the answer would be “yes”.