Imlanphere: In normal fwd flight, the airframe will try and rotate in the opp direction to the MRB, correct? If one increased collective(power), this reaction would try to increase(obviously we prevent it from doing so by applying corrective yaw pedal input). If one was to reduce the collective to almost a min pitch setting (auto) then the opposite would occur, correct?
Now, when the TR lets rip (!), then the airframe will immediately yaw in the opp direction to the MRB, correct? If you lower the lever fully (auto) then this dramatic yaw swing will be reduced (but not fully), correct? BUT, because your engine(s) are still switched on! the drive train will continue to transmit some power (torque) thru to the head thus the residual yaw will STILL be in the OPP direction to the rotation of the MRB. Now, when you switch the engines off....there is no REACTION thru to the MRB from the running engines, other, now than plain old friction, and it is this force which causes the airframe to attempt to yaw in the direction of the MRB's. This results in a further reduction of your yaw problem but will not completely remove it unless you are travelling with sufficient fwd speed to act as a wind vane also!!!
TR failure (fwd flight)will always provide you with a fighting chance if the engines are switched off. Leave them on (singles or twins) and you are dicing with death, literally!!
Throttle manipulation in modern helos (post twist grip) is NOT an option...
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Thermal runaway.