That is one scenario I have heard from someone who was in a submersible that that very thing happened to.
Having said that, I also hear the vehicle was equipped with a $40 wireless video game controller for steering. I wonder what other equipment was of a poor quality.
And they forgot to bring a spare battery ....
They could not open the hatch from the inside. It has 17 bolts that must be unscrewed from the outside.
So they could have made it to the surface and bobbed around while the oxygen ran out.