[Pierre]

I'm afraid they'll only be recovering bodies. I'd be interested to know what contingencies where in place to cover this situation.

They say they lost communications after two hours, I believe it takes longer than that to reach the site, which would suggest a failure with the sub as opposed to the sub being snagged on wreckage.

I would have thought such a sub/ operation would have:

1. Redundant power systems should one fail.
2. An independent battery powered transponder.
3. An umbilical to the surface vessel.
4. A duplicate sub on the surface vessel capable of retrieving the sister sub.

and I'm sure there are other mitigations that could have been in place. I know it's a risk doing this kind of thing but you have to cover off as many what ifs as possible, and a power failure must be the No.1 on the what if list.