Sorry mate but you are wrong. Once the torque on the failing engine falls below 400 ft lbs the autofeather armed light on the operating engine will extinguish indicating that the operating side autofeather is disarmed.
Groggy, that is correct and is exactly what I said - though in different words.
To the question of engine damage in the event of inadvertent autofeather:
An inadvertent autofeather will have no effect on turbine temperature but
may overtorque the engine.
At typical crusing altitudes the torque would get nowhere near the limit but the lower the altitude, the more likely the overtorque. At any altitude below about 5000' I would suggest it was an absolute certainty.