CEFOSKEY - A tail rotor drive failure from <800' would be quite difficult to deal with even when already pretty much in autorotation, though the report just says descending, not autorotating. With significant power on, the intial yaw would likely cause a serious upset. Looking at the pictures of the tail drive here,
if the tail drive pinion was in such a bad state, think what the rest of the gearbox would be looking like. You state "the torque should have been almost zero", this may be true (though probably not at the time of failure) but you are assuming no increased drag from a seriously damaged main transmission. In reality once engine power was removed there would likely be significant negative torque causing the fueslage to rotate anti-clockwise. The S92 is bus-shaped at the best of times, I don't think it has much weathercocking effect without a tail rotor going round. Most likely it spun, if not immediately, then as the speed was reduced in the flare.
HC