First, 120 kmph is only about 75 mph. Not very fast.
I think people have some misconceptions about t/r failures - namely, that the helicopter will weathervane sufficiently and you'll be able to maintain control. But, like everything in life...it depends. It depends on the type of ship you're in (e.g. length of fuselage ahead of the mast), your percentage of MAUW, the speed you're going and the amount of torque you're pulling. And maybe the phase of the moon too for all I know.
The tail rotor does more than just counteract main rotor torque in a hover. It also augments vertical fin area in cruise flight. We say that the canted vertical fin on the 206 causes the t/r to become "unloaded" (i.e. zero thrust) in forward flight, but that does not mean the disk area provided by the tail rotor is unnecessary.
The spinning tail rotor acts as a big flat plate back there. Whether it is producing any thrust or not, the flat-plate area of the t/r acts as a de facto vertical fin, augmenting the area of the tail boom and other vertical surfaces. Take away this spinning disk and you suddenly have less...much less...vertical fin area to work with.
Bell figured this out in the late 1980's. Then they revised the emergency procedures in the 206 RFMs. I don't have mine handy right and so can't quote it, but basically they said that if you had a complete loss of rotation of the t/r in cruise flight at cruise torque you could expect uncontrollable yawing accompanied by a nose-down pitching moment if you didn't immediately react to the emergency. Something like that. But they did use the word "uncontrollable" right yaw. As in, "not even the relative wind will stop it." And if that isn't a scary thing to think about in a helicopter with a teetering rotor system, I don't know what is. Because in a 206 in cruise, it wouldn't take much right yaw/left roll at all to get into mast bumping. Damn!
And it takes more than just lowering the collective - you've got to get rid of the torque RIGHT NOW!
We all imagine ourselves as being modern-day Chuck Yeagers with lightning-quick reflexes who would react instantaneously and snap that power off at the first sign of uncommanded right yaw. But I'm sure there are plenty of "average" pilots out there (and maybe I'm one of them) who would suffer a complete t/r failure and might just sit there for a few seconds as they try to comprehend and process what's going on. And the trouble is, in such a case you do not have "a few seconds."
Now, to the Hind accident. It would appear to the untrained eye that the tailboom and vertical fin of the Hind might provide generous weathervaning tendency in the event of a loss-of-rotation t/r failure. But maybe not, who knows?
That's a huge tail rotor, and perhaps the loss of its disk area might mean that the boom and vertical fin are not enough by themselves to prevent a complete 360 degree yaw. As I said, 120 kmph/75 mph is not very fast. Maybe they were pulling a lot of torque and weren't the sharpest Hind pilots in the shed.