I am not even sure why we are looking for them, I don't think there is any way to setup rescue equipment that can go low enough to help them and drag that submersible out of the water before they would run out of oxygen.
"It carries the Victor 6000 autonomous robot, capable of descending to a depth of 6,000 metres, beyond the 3,800 metres of the wreck's position"
https://www.reuters.com/world/europe/france-send-ship-titani...
Last I checked on MarineTraffic Atalante was about 100NM away from site. Would it not help?
All that is still theory, we don't even know if the submersible isn't already destroyed.
I've followed an OceanGate Titanic mission where a popular travel blogger was participating in and from what I understood there aren't many submersible vessels in the world able to go so low, let alone with functionnal tools. It is not like you can open the door to a diver for him to attach a cable, pressure is just too high.
The small submersibles used for Titanic the movie for filming the wreckage were Mirs* and a marvel of engineering for their time. However "[t]he level of technology flowing into the Soviet Union raised concern in the US and Rauma-Repola [the Finnish manufacturer] was privately threatened with economic sanctions."