Gulf of Thailand isn't so deep, at worst around 80m and not even that if the flight sunk enroute from the Malaysian coast to Vietnamese coast. If they crossed over the east coast of Vietnam then there's some deep water in places - ENC shows 100-200m soundings (confirmed by some of the platforms in the area operating in 180m water), until you cross the continental shelf and it drops off to 1000+ meters, even 2000+ meters a little south of Danang. It will really depend where they can pinpoint the impact site, but if it's off the shelf deep-sea recovery will be extremely difficult.
Anyone recall at what depth the AF447 wreakage was located in? Like Airbus, I'm sure Boeing will want know why this airframe went down if humanly possible - like the Adam Air B737 before.
Actually besides Bunga Kekwa A there's around 12 other platforms in the area and north of VungTau up the east coast is heaps more. Hopefully somebody sees something floating in the water.