Thing is; it stopped pinging when they were about halfway down. Power would still be mostly off, but sounds like all power quit if it couldn't even ping anymore.
So if they had no manual way to release ballast or inflate some kind of flotation it would have been a trip straight down.
Or it had imploded at that point. (About 6,000 ft. over 2600psi)
Then what to do think the banging sos sounds are?