Having repaired miniature electronic circuits after a ~ a day in salt water (while energized) I wouldn't hold out much hope for the cards in the recorders long after they have flooded. Pieces of the circuit trace just vanish. I wouldn't be surprised if individual chips lose their leads and corrode internally at that depth/pressure. All we can do is hope that the seals hold, that data is recoverable, and that the people designing the protective case generously over-designed the enclosure.
Those lost in AF447 deserve the chance to have their story told.