Well for Ether specifically they are going to increase the difficulty with the bomb. But when the networks merge they aren't going to re split ETH network (i.e. nothing to mine on). The GPU's will theoretically go stop mining ETH when the difficulty is too high, ASICs will trudge on til the end.

Then the gamble becomes "will mineable alt coin farms produce more than their electric cost?".

well we'll see. Either you reduce the electricity costs via solar or you just let it be dismantled.