Mistakenly pulled breakaway cable

I guess that I really don't see the concern about damaging the magnets. 3 amps at 13 volts is only 39 watts which is really nothing in heat considering that the magnet is solidly heat sinked to the brake drum. These components are made to work in a very hot environment.

I can't imagine an electric brake manufacturer designing a magnet that couldn't take that power/heat load indefinitely.

I would drive a short way and check the brakes with the controller. If they still work well then enjoy the rest of the trip.