As the search stretches on without success, I'm inclined to wonder if the loss of Comms might have been separated from the loss of the a/c by some considerable amount of time.
Is there a scenario in which something knocks out all Comms, transponder, etc. but leaves the a/c otherwise operational? Perhaps a fire, and the crew tried to troubleshoot for several minutes (or longer) until the flight control systems were disrupted?
Such a scenario might put the crash site dozens or even hundreds of miles from where Comms were lost.