I just can't think what if the engine wasn't at idle, the outcome of not being able to shut it down it had been really serious.
The engine on the QF32 was not at idle, it ran at the thrust setting at the time when the disc failure on the adjacent engine occurred during climb out. As I recall, the crew had to deal with this fact in calculating the landing distance required and maneuvering the aircraft to line up on the approach to the runway. They did not know the engine wouldn't shut down until the very end of the rollout when they attempted to shut it down.