Quite simply the A/C encountered Severe turbulence causing the autopilot to disconnect, normal procedure is to disconnect the autothrust and fly the aircraft manually.
There is a strong probability that the aircraft suffered a bombardment of hailstones if the severity of the CB's reported in the area are anything to go by which could cause engine failure.
This would account for the loss of the electrical system and eventual loss of cabin pressure as indicated by the ACARS messages sent.
With the amount of static in the area a mayday call on HF would be useless but to be honest with everything going on and severe vibration I doubt whether you could find the button.
With only backup for flight controls i.e manual rudder control and pitch trim, stabilised flight or recovery would be almost impossible with structual failure almost inevitable.