HF, I'm not descending into semantics; there are three different types of tailrotor system failure, each with it's own issues. You have grouped them into just two types.
Re. the Puma ditching: The Puma has five tail rotor blades. Running through the length of the hollow tail rotor drive shaft, is a push/pull rod. At the opposite end of the rod from the servo is a five armed "spider" (although everyone knows most spiders really have eight "legs", French ones perhaps have only five). At the end of each leg is a pitch control link, attached to control horns, one for each blade. As the servo moves the rod, the spider moves with it (it's bolted on), push/pulling on the pitch control links.
In this incident, IIRC, something between the servo and the links broke, giving fixed pitch, somewhat less than that required to balance yaw in the cruise. The aircraft began to yaw away from the MRG torque, giving very similar symptoms to a tail rotor drive shaft failure.
An unwitting pilot might have mistaken the situation for a driveshaft failure, in which case he would probably have auto-rotated and shut down both engines. In previous years there had been little in the Puma FRCs or Pilots' Manual to suggest otherwise.
This would be incorrect because the tail rotor was still producing some positive (anti-torque) thrust. Devoid of main rotor thrust, the aircraft would then have begun yawing in the opposite direction, possibly meaning the pilot would have lost control.
The only correct action, as taken by this pilot, was to reduce collective sufficiently to control the yaw. He kept the aircraft under control but unfortunately he had insufficient torque to mantain level flight. He was able to fly in a descending turn to the surface, whereupon they did a relatively gentle ditching and escaped unhurt.