I read an analysis of scenarios for the sub, and the best case is that they had a power failure but managed to surface. This is plausible because if something went wrong they would just need to drop their weights and float up naturally.
In that case, they're floating somewhere on the surface without communications and just need to be spotted.
But even that isn't a good situation because the ocean is ginormous and the sub is locked from the outside, so they're still limited to another day and a half of air supply.
If they're alive but under the surface, the search is nearly hopeless.
I read an analysis of scenarios for the sub, and the best case is that they had a power failure but managed to surface. This is plausible because if something went wrong they would just need to drop their weights and float up naturally.
I'm not sure dropping the weights would help from that depth. There's a point at which the pressure of the water above you cancels out any buoyancy lifting you up. It's not even that super deep for divers; I don't know what it is for a duct-tape-and-zip-tied backyard-crafted submarine, though.
If it's still water-tight, occupants wouldn't need to decompress since the interior is still near atmospheric pressure. If it leaked at 13,000 ft... the bends are the least of their worries.