I'm surprised the craft doesn't have a pinger, like airplane black boxes do (and those can survive on the ocean floor, too). 96 hours of oxygen won't help if it takes 200 hours just to find where they are.
They can survive on the ocean floor but definitely not ping from there.
The Trieste dive to the bottom of Mariana Trench were able to use voice communications from the sea floor. Should be possible from Titanics depths then, seeing as Mariana’s is 3x deeper. Assuming the sub hasn’t already imploded, that is.