I've seen articles that estimate the chance of rescue at less than 1% :(.
I would love to do something similar to this, but I wouldn't, because it's spectacularly unsafe (not to see the Titanic, I don't feel that's OK in a way, but to see sea creatures). I chose to go in a boat with a glass bottom instead. It also only cost about the same price as a meal.
I understand wanting to explore but if you have to sign a disclaimer that mentions the possibility of dying on the trip multiple times, and you sign away those rights... that to me combined with the way this machine is operated is really concerning.
But that doesn't mean I don't feel for them. Obviously they didn't want this to happen. People have criticised this making the news. It makes the news because it's unusual - yes, people die on the water every single day but when it comes to this story, it has captured the public's imagination because it is so unusual.