Protect battery from overvoltage - DC brushless motor overspeeding condition
I would consider using a relay (possibly a solid state type) that disconnected the motor from the drive electronics when the motor terminal voltage rose above a critical value. when the voltage dropped back to a safe limit the relay would reconnect.

If you need to load the motor (now a generator) in the over voltage state then this is also possible however, I see no immediate reason to make a load if the motor is disconnected via a relay.