Might the cause of the violent pitch down of this ill fated helicopter, be an aerodynamic stall of the right remaing half stabilizer ?
Indeed a bit strange that the 'simple' loss of one HS should lead to such a dramatic result.
Maybe it didn't simply fall off but twisted in a Nose Down direction. This could also possibly explain the massive excursion in Roll that occurred simultaneously?
At vne the Fenestron 'eating' the endplate should not cause massive Nose Down or Roll.
Still a bit mysterious...