Will a Curtis 1204 controller be damaged if a cable from the controller to the motor is disconnected and the throttle is cycled with voltage to the controller?
I can't say for certain, but I wouldn't expect that to cause any damage. I checked the manual and it doesn't list any warnings about that situation.
I do know that disconnecting a motor wire WHILE the motor is running will likely destroy the controller Mosfets. I've seen that happen before in a rather spectacular fashion.