Reading about these incidents is chilling, but something I began doing as soon as I hit ScubaBoard. Not to be macabre, but to learn. Even as a newer diver, I find myself taking risks (mostly out of compacency, not an urge to push the envelope). Reading these reminds me that it only takes once...
Thoughts and prayers to the family, and also to her cabin mate insta-buddy. Yes, she made a horrible mistake by surfacing and not informing her buddy, but from my limited experience with vacation hot spot dive charter instabuddies she didn't do anything that many (perhaps most?) vacation divers wouldn't have done. (Scary!) A lot of these problems revolve around the misconception by vacation divers that the DM is responsible for and intending to shephard the group.
Diver A was low on air and told to surface... so she does as she's told, thinking the DM will then take responsibility for her buddy, Diver #2.
Let's count the lessons.
1. Who is ultimately responsible for you? You. This comes down to every decision you make: where you dive, whether you dive, who you dive with, etc.
2. Don't hesitate to call a dive. A trip to Galapagos was probably a once in a lifetime thing. But it's not worth dying for. But let's be honest: too many people would have chosen to dive there anyway even if they were having problems of some sort.
3. Commit to being a good buddy when on a trip and insta-buddied up. OR, state the truth and say you prefer to dive solo if you won't accept the responsibilities. Yes, this may mean you'll sometimes be left doing all the work as not everyone will hold to the same standard, but isn't that better than the alternative? (I know I wouldn't want to be the person that has to live with the unanswered question of, "If I had just done one small thing differently, would that woman still be alive?")
4. It takes two to get separated. If your buddy disappears, you follow the protocol once you notice, and if they can't be located you surface, or you accept the risk and responsibility inherent in solo diving...not to mention pissing off and scaring the holy hell out of your buddy if they surface and... you don't. (Not such a deal in crystal clear water, but in bad viz like in the PNW... scary. The surfaced buddy is feeling pretty helpless.)
5. Unless you're paying a dive pro for their undivided attention with the implicit understanding that you are diving together, then they're just a tour guide. Period. (And even if they ARE your specified buddy, see #1). I could have died ten times over on my first trip to Cozumel and no one would have known for a while, despite my DM being "great" and knowing I was a newly certified diver (like... JUST finished cert the day before).
Who can add some more?