No expert here. I don't have any time in a 206, just a 205. I was investigator in over 1000 vehicle accidents as a State Trooper. LOL. I would not argue against your idea that a "progressive tear-away" could be a feasible explanation. I saw the video of the two large helicopters in Kuwait a few decades ago. They were straight & level in line abreast (side-by-side). Then they got inches too close and rotor tips started striking, barely. Within one second, the tailboom had folded and flew off the aircraft sending the fuselage spinning to the ground. The tailboom is very, very light and weak. It HAS to be. My point is, in the first few milliseconds of a "tear-away" event like you describe, the boom could be broken off.