I see little relationship between space missions and the recent sad event. Space missions are risky. But there is extensive testing of every part of the mission. There is a gradual incremental approach. Everything is done to mitigate the risk. There is always a lot learned by each mission even the incremental ones. There are hundreds of hours of practice of each part of the mission including by support personnel.
There is the common thread that when there is an accident if it was not totally unforeseen, then it came from getting over confident and ignoring warnings from the experts (challenger).
I do not fully understand the question. It is way too vague and is asking for absolutes. I did not answer it.
A record depth dive that is testing out new equipment that has a good chance of success might be reasonable. My scifi brain can envision a drysuit material that goes rigid at depth and a chemical plant on the back that could extract oxygen and some needed materials from the surrounding fluid. Not existing now but 100 years from now who knows. Testing dive gear for Europa?