My bet would be that one of them would simply make up some new rules, then attempt to enforce them, probably claiming that since the WTMD is broken, all passengers must pass through the AIT.

They'd probably still try to claim that opting out of the AIT isn't allowed (but TSA employees have been lying on that topic for months, now) and threaten the "Do you want to fly today?" to anyone who refused.

The actual WTMD-failure procedure is probably claimed to be SSI, assuming such a contingency plan exists (but until "intelligence" claims that Al Qaeda is going to deliberate disrupt electrical systems in airport terminals so they can sneak "forbidden threat items" through the checkpoint, I doubt anyone's actually written any such procedure.)