TC,
Without sounding too critical....you do make some statements that may not be as certain as you present. As written some of your comments border on deadly unless someone with experience knows when to skip along.
If you experience a Tail Rotor failure that leaves you with too much Tail Rotor Thrust.....doing an EOL is the exact wrong thing to do.
Catastrophic TRF: If the tail gearbox departs flight, the associated change of CofG will almost certainly cause the aircraft to pitch out of control due to the (weight x moment arm) change caused by the removal of “x” Kg of metal at the end of that moment arm. ENDEX.....
Not so fast.....you might experience a complete loss of control along with the shift in CG....but the Exercise is just beginning.....not
ENDEX as you suggest.
An IMMEDIATE full reduction of Collective, and if that doesn't work well enough, Engines(s) to Idle.....and attempt to regain control of Pitch/Roll/and see if Yaw control no matter how limited is regained. If you get the aircraft upright and responding to cyclic inputs.....reapply power and collective and see if you can maintain flight(if necessary) and if unable....or if there is a very good place to land.....do an EOL expecting yawing at the Flare/Decel. That might be checked with a bit of collective.
Remember the Bell 412 Crew in the GOM that had a TRGB and Blades depart the aircraft at night over the water. They said they went inverted and spun.....but were able to regain control after bottoming the Collective and rolling the engines to Idle....then were able to fly the aircraft until they decided to carry out an Emergency Landing.
It might be extreme....but don't ever quit flying the aircraft....fly it to impact but fly it.
TRF in fwd flight results in uncontrolled yaw in the opposite direction to main rotor rotation.
I prefer the use of the word "Un-commanded" rather than "Un-Controlled" in that the weather vane effect of the Tail Fin might limit the Yaw to a large side slip angle but not wind up in a spinning of the aircraft with a bit of airspeed.....thus is is "controlled" but remains "un-commanded".
Analysis of Tail Rotor failures other than Loss of Components can be a lot simpler than what you set forth.
Power Pedal forward.....Good Day. Power Pedal aft.....Bad Day.
The problems that leave you with too much Tail Rotor thrust can be addressed by reducing Tail Rotor RPM then making a shallow approach to a hover.....during the approach the nose of the aircraft will be off to one side and as the airspeed lessens will begin to come back towards the direction of travel. Hold adequate airspeed to control keep the Nose off to the side until you can get within 1-2 feet of the surface. If you plan the approach to arrive at a very low hover (1-2 feet )....as the Nose centers.....simply lower the Collective and land on.
If you miss judge and the Nose swings past the direction of travel....simply accelerate and try again.
If you have too little Tail Rotor Thrust....the choices are a running landing or an EOL. As groundspeed might be excessive to maintain yaw control and thus make for a very dangerous situation (you are hitting the ground at a very high rate of speed, with full power on the rotor system, and your yaw control is very limited), the EOL offers a lot of advantages. In the EOL you arrive a little or no ground speed, the engines can be in Idle or shutdown, your ROD will be slight after cushioning the landing, and if the aircraft yaws and even if it rolls over....the resulting forces are much less.
Even without a Tail Rotor....the Pilot remains capable of "Controlling" the Yaw of the Helicopter by varying Torque on the Rotor System and Airspeed.
The failure most Pilots make....is not fully understanding the effect of the various controls, levers, throttles, and cyclic have on "Yaw" in their helicopter. This is something that needs practicing, so that when an failure occurs, the initial response is automatic and the subsequent actions are based upon a thorough knowledge of the way the Helicopter reacts to the controls without benefit of the Tail Rotor.
You laid out a lot of information that will certainly get the discussion going....and is an interesting topic for you to bring up.