All I know is, I don't want to be anywhere near any open water.

There is nothing that exhilarating about this. yes most of the people got back on the boat because they were being overly cautious and wanted to stick close.
Which is what I would do.

But Dan and Susan were a couple of smart alecks. They were so sure they knew more than anyone. You could tell that they each wanted to stay home and deal with work. If only they had done that.

Their relationship was boring and troublesome and they wanted adventure so they went. The whole trip seemed like a trial to them.

Instead they found they really loved each other at the end when they only had each other.
Of course they were to blame for straying so far away and not obeying the rules.

But how in heck did the stupid guy count wrong>? How about checking for each person's gear or calling out all the names and when someone doesn't answer,,,they are not on the boat.

Simple.
I hope that diving company went under.