If the sub had a pressure hull fail they’d never know what hit them.
"If there is an implosion at depth, the compression heating caused by the ocean rushing into the hull would be sufficient to heat the air inside to hundreds or even thousands of degrees. Under such circumstances, any flammable object inside (grease, clothing, people) would likely ignite or detonate ('Diesel effect')."
“If the sub had a pressure hull fail they’d never know what hit them.”
But if they are on the ocean floor next to their launch platform waiting for their 96 hours of air to run out - not good.
How about a tiny hole or a bad seal in an observation port. Water comes in at 5000 psi pressure slicing thru anything in front of it. Then slowly the cabin fills with water, electricity is lost and they drown, ultimately assuming ambient pressure and temperature on the bottom.