If they did somehow find themselves outside the sub they wouldn’t be crushed. The human body is more than 60% water which isn’t compressible and a quick google suggests that you’d have to be more than 35km down to be hurt by the pressure.
Having enough air to get to the surface would be one of the may issues as you’d have to be breathing something very exotic at that depth plus you’d need many very long decompression stops on the way up along with a vast quantity of gas.
Pressure cylinders – I’m no expert but some types of scuba cylinders are 300 bar and they do carbon versions as well. I know its a much smaller scale but the technology exisits.