Even if the boxes are found. The CVR reveals nothing, The DFDR reveals a more precise version of what we roughly already know?
This was very intelligently planned by someone(s) who did not want the facts ever to be revealed??
Presuming the CVR is of the two-hour, looping variety, only the last two hours of cockpit activity would be recorded. The only way the CVR would have anything useful would be if someone was still alive and talking for the record.
This presumes no one opened the CVR circuit breaker at any point. If someone did open the breaker after a deliberate diversion was complete, perhaps to ensure a record of what happened in the cockpit, useful information may still be available.
If someone did open the breaker after the diversion began, it's also possible they closed it at some point when it was obvious there were less than two hours remaining until flameout, then made some kind of a statement.
All of which presumes MAS370's diversion was deliberate, not an accident.