212Man is right, this speculation has gotten way out of hand! One has to believe something very bad happened very quickly to cause this thing, and that small splash in the press photo shows something probably nowhere near controllable. Other than that, we must wait for the vast amount of data to know what happened.
Regarding the S76 family AP's. they will not suck the rpm way down, since the engine limits are monitored by the FD/AP, and the collective cue is limited by limit engine Temp or Torque. Since the Nr drops when the remaining engine exceeds those limits, the Nr will stabilize in a very comfortable place if an excessive OEI climbout is attempted.