Without trying to predetermine the cause of this accident, I have the feeling that poor old BC has picked up an enormous amount of ice, probably more than the aircraft can handle, has probably turned away from the area, as you would, and due to the increased weight and higher wing loading put the aircraft in an over stressed, unrecoverable position which has caused the aircraft to break up.
You have to have experienced the massive ice build up that can occur in the Paraparaumu - Otaki area to understand where I am coming from and I suspect judging by the conditions that were in that area at that time, that severe icing may have been the order of the day.
It is not a nice experience to have a massive ice build up, which can occur in seconds, even with the deicing working overtime, and feeling the the approaching buffet of a stall.
The only recovery I might add is to descend gaining whatever speed you can, without turning to prevent increasing the stalling speed, until you have sufficient speed to safely turn away.