With regards to recovery, a typical N Sea spec WROV can operate down to approx 2500m and is capable of tasks such as recovering a FDR. There are a number of vessels operating on construction projects in W Africa at the moment equipped with such ROV's, any deeper than that however is getting very specialist.
Even so, recovering a whole aircraft from that depth is one heck of a feet and I would suggest extremely unlikely due to the massive costs involved. A hi-res multibean mapping of the debris field along with a visual ROV inspection of key areas and recovery of the FDR would be more likely.
Fingers crossed it doesnt happen like that and by the grace of god they find the kite merrily floating on the surface with all the pax and crew safe and well.