@crippen
Could not the memory module still be there and buried??
Yes, it looks like it could be there, but no doubt once it was turned over by the submersible, the truth was revealed. I think why we can see more of the PSU and drive electronics box in the photo is due to the crater surrounding the box, formed at the time of impact. The fact that there is no crater under the chassis which supports the memory section, suggests that the memory section is missing. The memory module, as can be seen from the fixings to the chassis, is designed to detach with minimal force in order to be free of any constraints and be able to survive becoming trapped and crushed amongst collapsing structures during high G impacts - hence the choice of spherical or cylindrical construction. However, like in any design, there are trade-offs, one of which is size, governed by the amount of fireproofing insulation needed to protect from high temperatures, and recognition - it's no good having a survivable device if it's too small to be found in wreckage. With the latter consideration in mind, the FAA standard for crash protected enclosures is to apply minimum dimensions for major axis.
For the elliptical cylinder example; the major axis (a), minor axis (b), and length (c) of the enclosure, must conform to the relationship:
a, b, c >= 2.0 inches
a + b + c >= 9.0 inches
The same applies for a rectangular shape, while for spherical shaped enclosures, the average radius must be => 3inches.
Given that the memory unit and the chassis have different shape form factors, I would be surprised if they arrived at the same location after a 4Km descent. Dependent on the CG & mass to vol, the cylinder/sphere is less likely to plane than the chassis (tumble maybe) and so will probably be found near heavy items from the empennage.