Very distressing incident and one that I am sure will be hard to pin down the causes of any time soon.
As to the recovery of Data and Voice recorders and parts of airframe and engines then in addition to the oil industry vessels there are ships that maintain/repair undersea communications cables that carry the internet around the world.These vessels have remote controlled submersible vehicles and can lift modest weights from very great depths as the cables lie on the ocean floor. They are also pretty good at locating objects on the sea bed as the cables are only an inch or so thick but of course they would need a reasonable prediction of location so as to limit the searc area to practical dimensions. Unfortuneately even if there is aposition report in the last ACARS message if thatwas sent at cruising level then the radius of probaility as to where the aircraft hit the water is pretty large and compounded by currents and water densities which mean that something entering the seas surface does not sink verticaly downwards very often so it will be a real challnge to locate any wreckage but not impossible.
Location and salvage/recovery will be a very expensive and time consuming exercise but I would hope and indeed expect that it will be seen as a critical activity in order to avoid future incidents, maintain confidence in what seems a very sound design as well as to learn as much as possible from whatever specific causal factors are associated with this accident