Several men who previously dove down to the Titanic have discussed the very real risk of getting tangled/fouled in the ship’s wreckage. The men also discussed the issue of prolonged exposure to cold temps at depth in a sub. We don’t know what has happened to the Titan sub.
How they avoid hypothermia and keep the CO2 level in tolerable range is as tough as the O2 running out.
I’m not optimistic. The sudden loss of contact halfway down is ominous.