Do they have an accurate current location? If not, that's the 1st problem they need to solve. Everything else is secondary.
They have no information on the location. Honestly the moment they lost comms and could not restore them I find it extremely unlikely someone in charge did not already know this submersible was a lost cause.
Given in a power loss it is supposed to automatically surface I would assume it has a means to broadcast its surfaced location in such an emergency.
That leaves only the likely result of it continuing to sink after the loss of comms.