They could redesign the brakes so that they are normally fully on and elictric power is only needed to hold them off. Some bird's feet work that way
As do pretty much all trucks. Lose air pressure and your breaks are locked on.
Not sure that having brakes' locked on' is a good failsafe. Just as hydraulic systems have an accumulator which will provide a set number of braking actions, surely the redundancy here would be to have an 'electrical accumulator' (known as a capacitor) to power the brake actuators when all else fails.
If the capacitor has any spare electrical capacity it could also run a redundant anti-lock system too. :-)