The only thing that could cut off all communications and all electrical power, followed by silence could only be some form of catastrophic structural failure.
That aircraft had damage history, a collision with a 747 while taxiing.
It could have placed un accountable stress on the starboard wing root fittings, that decided to give up while in cruise. due to some CAT how ever light or severe as the case may be.
If the airframe went into a structural failure dive towards terra firma or water the crew would be a little more than a tad busy during the horrific descent, and would not have been able to send a radio message or mayday.
