There's nothing to say about the sub. There were no measurements and no black box. It was all a 'handyman special' and the captain went down with the boat.
As proven by the shuttle-like disasters, there were many single points of failure that combined to give a the odds of catastrophe at about 1 in 100 per trip. What if the whole thing were engineered to meet safety code, like window washers?
As I've seen with industrial safety, every local shop is perfectly happy with 1 in 100 odds. However, there are so many shops that somebody would die every other week across Ontario. This is bad for government and the economy. So, Society has dictated this is unacceptable, and the odds are forced to be 1 in 10,000.
That's a tough slog and requires lots of inspectors. Everything gets an added backup, like finger-guards, signage, etc.
What would we do for a sub? Early subs all went down like stones in a pond, until more safety factors were added. Airplanes in the 50's lost wings because of fatigue. This sub had a shell of carbon fibre, and I was surprised about that. An engineered sub would be 5 times more expensive. For commercial operation you only want components stressed to 10% of capacity. If you go more, like racing cars and fighter jets, then you need a comprehensive monitoring and replacement program, which is all even more expensive.
I'm sure the sub shell went 'crunchy crunchy' every time it went down, and that was shrugged off. But that's the sign of fibre fatigue. I would have had that all monitored, since you can't replace the shell. However, this is all moot, and we don't learn a thing from this. Since there is no physics any more, we can expected lots of learning with the next big earthquake.