Yeah the sad part is that, really, the best we can hope for is a post mortem. Rescue is almost impossible in this situation.

Something this small could simply be floated to the surface. With big things there no way that can be done. Still difficult af but possible, don't know if things like that already exist.

Only the most optimistic guesses about their air suggest there is any left in it at this point. We're pretty much at the recovery phase.