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Today it's mitigated by the pilot. Runaway Stabilizer is a memory-item. [1]

This is the same memory item Boeing thought would mitigate MCAS, since that is essentially a runaway stabilizer trim, although in retrospect behaving in a very different manner making it much harder to diagnose.

[1]: http://www.b737.org.uk/runawaystab.htm

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Runaway Stabilizer / MCAS cases can be mitigated by the pilots (they can use cutoff switches and do manual trim), but not this kind of electrical short:

> Furthermore, the electrical power in that wire could circumvent the cutoff switches in the cockpit that, in the event of such a stabilizer runaway, are used to kill electrical power to the tail. Theoretically, the pilots could be unable to shut it off.

It's not a great mitigation, but the last thing on runaway stabilizer's memory list is to "grasp and firmly hold" the stab trim wheel.

The electric motors can apply more power than a human can resist. So that's not exactly helpful.

I believe there is a clutch mechanism. There are videos on YouTube of pilots doing this (in a simulator.)

The system is engineered so that an operator holding the trim wheel wins, via a clutch mechanism.

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