Seems to me that the vehicle should be big enough to find, but small enough to retrieve.
Hard to believe the men are going to be left there in it at the bottom of the sea.
They won't be. Heaven and Earth will be moved to retrieve the bodies. They are only halting rescue operations.
And in 100's of feet of water, yeah, some divers (presumably the SAR kind) cannot go that deep. Other divers (and certainly immersible craft) can.