I may have misunderstood the questions here, but there are some fundamentals about helicopters that may have been missed.
Following a tail rotor failure, or TR drive failure, the helicopter can still be controlled
under certain circumstances. If the airspeed is sufficient there will be a large proportion of the anti torque requirement provided by the vertical stabilisers, and the pilot will be able to fly to a running landing on a suitable surface.
Turbine thrust is quite slight: if it were not for the exhaust temperature, on most helicopters you could easily put your hand into the exhaust and hold it there, the flow is so low. Westland modified the Gems on their World Speed record holder (Lynx) to use some of the residual thrust, but from memory it was quite low.
"Free power turbines" are used in helicopters, whereby the air is effectively a fluid clutch between the power turbine and the free power turbine. As the airflow passes through the last power turbine stage, it then hits the free power turbine, which is mechanically separate to the compressor and is driven purely by the final stage of gas. This powers the engine gearbox, which has various outputs including a drive shaft to the main rotor gearbox.
In the event of a power failure, helicopters enter autorotation and the engines are disconnected via the freewheel unit in the drive train. The main and tail rotor gearboxes are mechanically connected, and the airflow through the main rotors keep the rotors turning. Autorotation is essentially energy management, where three types of stored energy (airspeed, height and rotor RPM) are managed to control the descent until the helicopter is flown to a suitable landing area, and a near zero speed touch down achieved by sacrificing the stored energy.
Simple, really
