How is it tautological? Some form of it is the very basis of atheism.

Doomsday timelines have lower numbers of observers. In all timelines where you are no longer an observer,i.e. all current doomsday timelines, your observation has ceased.

To repeat myself: if there is no life to experience doom, then whatever happens still happens, but it is not "doom". In other words, doom is a moral construct. Morality only exists when a being draws a line between "good" and "bad", it is not a real thing that exists.