Even if black box is found, it will most likely just be silent...

Even if black box is found, it will most likely just be silent recording and then the sound of a splash.

Black boxes only keep the last two hours of a flight.

What do we expect to hear during those last two hours?

Every theory presumes that everyone was dead 2 hours into the flight, or everyone besides the pilot.

Unless the pilot was alive and flying, and decided to make some sort of confession, which he probably didnt given the lengths the plane went to prevent anyone knowing what it was doing.

If it was an accident and the plane just kept flying for 6 hours with 239 dead passengers then obviously nothing much is going to be on the talkbox.