Nesov says rescue sims are impossible, while you only say my FAI scenario is unlikely. But you claim to be thinking about the same UDT. Why is that?
I don't say rescue sims are strictly impossible in the above argument, indeed I said that everything is possible (in the sense of being in the domain of prior, roughly speaking), but you anticipate only a tiny fraction of what's possible (or likely), and rescue sims probably don't fall into that area. I agree with Carl that your FAI scenario is unlikely to the point of impossible (in the sense of prior, not just anticipation).
This is our monthly thread for collecting arbitrarily contrived scenarios in which somebody gets tortured for 3^^^^^3 years, or an infinite number of people experience an infinite amount of sorrow, or a baby gets eaten by a shark, etc. and which might be handy to link to in one of our discussions. As everyone knows, this is the most rational and non-obnoxious way to think about incentives and disincentives.