Okay, now that was good to know! This could easily happen to DT as well if you put your rad outside.. Although 24 GPUs would draw about 1060w while idle so there would still be a good amount of heat going in to the loop but if the fan blowing through the the rad keeps running full bore after the net is out temps would still drop rapidly and low.
A kill switch shouldn't be too difficult to do.

Ek blocks are half plastic but condensation would still happen on the steel plate some of the blocks have on top(5870V2 & 7970). Some condensation would also happen on the sides. I think the under side facing the card is getting some heat  and the air doesn't move there as much so it is probably ok.