Prawn2King4 - with a tail rotor hardcover to full pitch autorotation will make things much worse. In this situation, at low speed, you need as much torque on the rotor to counteract the maximum anti torque from the TR.
As the TR is at maximum pitch, AUW, MR torque, density Altitude and wind direction against the anti torque moment are all relevant but combined, may not be enough to overcome the anti torque moment being generated and a yawing spin may be inevitable.
Turning the engines off removes all the MR torque and the yaw rate would dramatically increase and most likely result in an uncontrolled crash.