cenzo, I totally agree. I added the final sentence on my post for precisely that reason.
This, on the face of it, is a highly unusual accident scenario (with unusually tragic result). I'm sure all the evidence exists and can eventually be pieced together by the AAIB, whilst we here are merely trying to make something of the puzzle without all the pieces.
Skadi, yes, a loss of tail rotor authority (to low anti-torque power) could of course give similar symptoms to a loss of drive, albeit without sparks and no unusual noise. But if that was the case here, it wouldn't explain the witness report. Also the loss of drive at either end of the shaft could have occurred and this would be perhaps less obvious from the photo. I did notice that the entire tail empennage was no longer fully attached to the tail boom. Close mechanical examination would soon make this clear and I'm sure this is/was a priority.