As someone who has been flying helicopters for a living for almost four decades, the prospect of this type of tail rotor control failure has always greatly concerned me.
I've been writing about it on this forum and elsewhere (initially when I flew RAF helicopters) since the mid 1980s. Some would say I "bang on" about it, but imho with good reason. This situation is a helicopter pilot's worst nightmare. Tail rotor control is completely lost and the tail rotor pitch then goes to either full power at "push" or "pull". I don't know of any present helicopter where this situation is recoverable by the pilot, whatever his level of skill and experience.
The answer is to mandate that by design that all helicopter tail rotor control systems are equipped with a centreing device for the servo valve mechanism, to prevent a servo runaway in the event of the pilot's flight yaw controls becoming disconnected, such as now appears to have occurred here. With such a device fitted, the servo is automatically biased to move to a fixed, central position enabling controlled flight to still be available and a safe landing of some sort to be carried out.
Some aircraft manufacturers, such as Sikorsky, having been fitting such devices to their aircraft for many years. Other manufacturers, as appears to be the case here, obviously still do not.
These devices are not difficult to design. Most consist of a simple spring mechanism. The simplest one I've seen (Super Puma) consists of something that looks very much like a bicycle tyre pump, with a spring either side of a piston, sitting inside a cylindrical body. The body of the device is attached to the aircraft structure and the "piston rod" is attached to the servo control valve arm. The piston rod moves in and out of the body under the influence of the normal movement of the servo valve mechanism, such as when the pilot moves the yaw pedals. As it moves it compresses one spring and relaxes the other and is "invisible". However, in the event of a pilot's control input disconnection (e.g. a cable break), the springs equalise to bring the piston to a central / neutral position, so that the servo valve cannot not run away. The Sikorsky devices I'm familiar with are slightly more sophisticated and consist of quadrant arms controlled by springs, but the devices all work in a similar way.
Had such a device been fitted to this 169, the outcome might have been very different.