electrotor
I stand corrected in my use of loose terminology. Perhaps it would have been more correct to state that the weight of the aircraft is primarily supported by the top bearing in the gearbox casing and as has been previously demonstrated, it is possible for the rotor shaft to pull through the bearing and depart given certain fault conditions.
This accident bears remarkable similarities to the G-REDL incident where the main rotor also departed from the helicopter. I would not be surprised if a similar failure mechanism was found. Height at which the incident occured is almost identical and apparently there was no warning before the main rotor broke away.