Re the A330, the question is obviously moot, since neither would float anyway. We can only hope they broke loose, so there is a chance of hearing the ULB.
Gathering other info reguarding ULB operating specs from previous posts, they are designed to function down to 6k meters but have effectve transmission of 1.5 to 3k meters of emersion. Even if they broke loose they would still sink.
As you agree the question is moot.
The two solutions are acms transmissions prior to power loss/elec. systems failure or increased ULB transmission capabilities. Seems I expect no FDR recovery in this incident.