If the instructor, the oil executive, anyone had, and they stayed together, it would have been over quickly. I don't know about registering a PLB in your country, I suppose it can be done it varies with countries, but even if a foreign registered PLB had been activated, then communications could have happened. The locals were already looking for them so the state department that got the original alert could have sent messages to tell them where to find them.
If no one had reported them missing, things would have worked much slower as 90% of PLB alerts are butt-dials, but things still could have developed. I still think that the first thing to do in such a case is to tie all divers together into a group. As someone mentioned, reg hoses tied to D rings would work. A group is easier to spot than a single diver, and then you find them all.
Yeah, having a meth-head for a driver was very unfortunate, but at least he did report them missing instead of running away.