UPDATE
A ship with two underwater vessels capable of searching for the missing sub, has arrived at the scene.
I'm not sure how they can raise the sub though should they find it.
Enough oxygen for 96 hours. Guessing you'd just go to sleep and that would be it. Lots online now about this sub having no controls other than a playstation style joystick to control it. If they're stuck on the bottome I think they cant be rescued, but there is a good chance they've managed to...