I can think of several reasons why the "zero torque" situation can happen....starts with a huge "BANG" and a loosely joined set of extremely spare parts. At some point in the break up of an aircraft...assuming the recorders are still doing their thing....would not that be an indication we would expect to see?
As what led to that break-up.....is anyone's guess.
The engines could still be running...but not connected to anything...or connected to something but the rest of the dynamic components have departed for other places...again...no torque needed.
The 76 is very slippery at high speeds...as is the 109....even the venerable 412 can be a hand full when the AFCS kicks off at high torque and airspeeds.
Airline pilots undergo "upset" training....do helicopter pilots? Or is that another one of those "verbal brief only" items on the check ride?