Bang or no bang
If I was going to have an engine failure in a helicopter I think I would be far more likely to know what was going on with an engine failure that happened quickly and preferably with a loud bang rather than one 'giving hints' as to its future demise. WHY - because its amazing how massive hints can get ignored.
True Story: I am in command of a high performance fixed wing aircraft at the threshold ready to take off on a 800m strip. Been flying these toys for 20 years or more. Power checks fine. Start roll at full power. 2 seconds later engine note changes and then recovers. Cant read any instruments due to severe vibrations. I somehow convince myself its OK and continue the take off. Result: clearing the trees by 100 feet instead of 800 feet.
My mind played tricks on me. It took me over 30 seconds to realise that something was definately wrong.
Landed without incident. Problem would not appear for engineer. Engine cleared for flight. Problem found 5 flying hours later. Fleck/flake of metal inside injector occasionally blanking off fuel flow to one cylinder = one draggy cylinder.Engine note recovery was the constant speed propellor reducing pitch to maintain revs. Realized if it had not been a severley overpowered little aeroplane in the first place [and capable of decent performance with one cylinder out] I might have hit the trees.
I wonder whether a partial engine failure like this happening in a helicopter could have similar effects on the pilot. I guess it would translate so... engine power reduces, vibrations, pilot or correlator reduces pitch to maintain revs - helicopter no doubt starts decending and wont thave enough power to hover - but are you going to realize that with the likely confusion.
Hence I just rather it go bang and I can get on with the auto.