. . . Even if SHA-256 is partially broken (say easier to find hashes, but not fully broken) . . .
. . . If SHA-256 is ever broken, it won't matter much what the ASIC miners had planned.
If it is only partially broken, we'd just see the difficulty increase substantially. Beyond that everything else would remain the same until/unless there was an effort to replace on the the hashes in the series. If that happened, I assume there would be an effort to replace the SHA-256 hash in the generation of bitcoin addresses at the same time.