Having done a vast amount of stability flight test in several helicopters, including the S76 series, I find this entire line of speculation factless and groundless.
1) Switching the dual AP off in high speed flight will not cause any awful response. Could the Charles Lindburghs who think so just try it to see what happens?
2) A simultaneous (within 1 sec) dual engine failure or a dual stability failure is virtually impossible, unless you do it on purpose, even if a self-appointed expert thinks otherwise. Unless you deliberately turned them off together, they will not fail at the same time.
3) The Tail Rotor does not cause any wild roll in an unstabilized S76, all you have to do is let go of the stick to see that.
My Lord, we have entered that black hole that accident investigators dread, where the "could have happened" starts to dominate the scene, in the absence of real knowledge and real understanding.
Give pprune a D- for this thread.