It is interesting that doomsday argument proponents seem to challenge our usual way of doing inference, by preferring an extended state space where we explicitly model the idea that "I could have been you." However, if we try to do this in a physics-oriented way, avoiding describing states directly in abstract features of interest to humans but not the universe, we get seem to get the same chance of doom as if we hadn’t extended states at all. Humanity may in fact face doom soon, and we have many reasons to be concerned about this. But I do not think the doomsday argument is one of them.
The bottom line: You still have to save for your retirement.