Interesting discussion. Air bags are used all the time in the recovery of sunken vessels, usually in shallower water. As stated before the depth (pressure) pretty much makes recovery of deeply sunken vsls near impossible. Sure it could be done, but at what cost? And there are definite safety factors to be considered. All in all it wouldn't be worth it.
The best way to go about it would be to place air bags within the structure of the ship (displaces water) and uses the ships own superstructure as a control factor (lessening the number of cables needed (the less amount of lines in the water around propellers the better)). Lightening the load prior to bringing her up (water weight vs. cargo/unnecessary gear weight). Bottom suction calculations, deterioration of the hull, achieving neutral bouyancy so she doesn't come up like an emergency breaching submarine and crack into pieces when she hits the water. There are a lot more factors to consider.