This question might not be appropriate as it is philosophical on a similar level as the Schrödinger's cat thought experiment. In any case it might be interesting to think about it nonetheless.
The reason why I put it here, is to get the thoughts of others on it, as I don't really know what to make of it.
Ok. The main assumption (1) is, that there is no live after death. That is, when an observer is dead, thats it. There is no path for her afterwards.
Now consider the many world interpretation (2) of quantum mechanics, in the way that all possible alternate histories and futures are real, each representing an actual universe.
I would argue that under these assumptions and solely from an observers subjective perspective, the observer is actually immortal then. In contrast, the worlds behave normal for everybody else.
To see that lets assume that an observer plays Russian roulette with a single bullet in a revolver with a revolving cylinder that has six chambers. The observer has a 1/6th chance for the bullet to be fired. So from an outside observer, in one out of six shots she will be dead, statistically speaking.
However from the perspective of the observer, who uses the gun, she can never travel the future path, where the bullet kills her, under the death assumption (1). So she can never find herself in a universe, where the bullet was fired. But according to (2), she will find (a copy of herself) in a universe, where the bullet was not fired.
Now I would argue, that the playing observer herself, never experience the bullet to be fired. Because this might be a future path for the external observer, but not a future path for herself. She will always find herself on a path, where she actually exists.
We can make this even worse, by loading six bullets into the chamber. Still there is a slight chance for her to survive, as there might be a misfire. From the outside we will see her dying almost every time, but subjectively the only path/universe she could find herself in, is the one with the misfire.
We could make this game arbitrarily silly by making her survival chance ridiculously small, however according to the rules of QM there will always be chance to survive. It doesn't matter how small the chance is. Altogether this should mean that subjectively, no one can die under assumption (1) and (2), or can we? At the same time, this is completely unobservable from the outside.
Ok. I think you get the idea. What do you think? If this is inappropriate for physics.stackexchange, suggest another board then.