Also, even if there are a lot o unfriendly AIs out there, a friendly one would still vastly improve our fate, whether by fighting off the unfriendly ones, or reaching an agreement with them to mutual benefit, or rescue simulations.

One potential option might be to put us through quantum suicide - upload everyone into static storage, then let them out only in the branches where the UFAI is defeated. Depending on their values and rationality, both AIs could do the same thing in order to each have a universe to themselves without fighting. That could doom other sentients in the UFAI's branch, though, so it might not be the best option even if it would work.