Only way to find out is with a seine and with water temps the way they are that of course wouldn't be a good idea.

I say there are survivors. From my experience perch are tough fish. If they can still grow normally at 3.5 mg/l which would stress other fish and put them off of feed, then it's entirely plausible they can survive 2.0 mg/l for a short period of time.

Perhaps the survivors would be candidates for selective breeding for fish that can tolerate higher water temps? Or get s shipment of fingerlings via air freight in the future from a North Carolina hatchery where they alledgedly can tolerate warmer temps?

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.