All that information would be sufficient to identify root cause, and remove a lot of speculation...
I think there is a pretty clear consensus that the track taken by the aircraft was the results of deliberate human inputs by someone familiar with the aircraft systems.
Now those on this forum who fall in this category will know precisely where to look for the CB which will render the quoted assumption invalid. I have already suggested (but was modded out) that the most likely scenario when/if wreckage found is that FDR recording stops at/about the same time the transponder was deactivated, and the FDR will contain 2 hours of silence.
Of course there is a slim chance that the FDR/CVR and possibly some other non-volatile memory from aircraft and passenger devices might yield some useful clues. Memory chips are enclosed in a fairly robust plastic casing, while the external contacts will corrode, the actual encased chip has a good chance of remaining undamaged. I know of several cases of lost / damaged underwater cameras retrieved with the sd card retaining the photos taken after a couple of years spent underwater.