The good news is that this pruning heuristic will probably be part of any AI we build. (In fact, early forms of this AI will have to use a much stronger version of this heuristic if we want to keep them focused on the task at hand.)

So there is no danger of AIs having existential Boltzmann crises. (Although, ironically, they actually are brains-in-a-jar, for certain definitions of that term...)