Except alternate timelines are impossible. The only convincing argument for multiple timelines is the argument for branching time. Branching time would entail timelines where objects within the branches would arise ex nihilo. Thus, branching time is impossible.
None of this is a concern if the computational theory of mind is false. I believe CT is false; therefore, I don't believe AGI is possible (it's a big ol' diamond with a tilde next to it).