Umm, an engine manufacturer can tell you what a severe engine failure is.
It's up to the aircraft manufacturer to tell you the pro and cons of how to treat the symptoms using aircraft instruments and controls.
So what do they recommend about a silent gear box failure where all that happens is the EGT drops to nil, the generators and hydraulics go dead the N2 may or may not go to zero (no signal??) but the N1 drops to windmill.
IMO if your actions might aggravate a failure condition then it ought to be specifically covered in the manuals.
So consider what can go wrong when you answer