I had a situation at a tropical destination. We had our DM, and 4 divers, a married couple, my buddy and myself. The couple was your typical vacation diver from the northeast, probably getting in a dozen dives a year on a good year.
The dive plan was the first diver to 100 PSI would let our DM know, and we'd make our way to the exit. Things got interesting when the husband let out guide know that he was at 600 PSI @ 60 FSW. The DM pointed to him then up emphatically, like he was saying "YOU UP NOW". My buddy and I looked at each other and almost in unison, we thumbed up too. So the three of us went up together, doing an open water ascent, leaving the DM with the wife. The ascent was uneventful, we all made a 3 min safety stop, then had a 200 YD + surface swim to the boat. (No good deed goes unpunished.)
The DM got to the boat shortly after we did, but no sign of the wife. He left her to do her safety stop alone on our mooring line. The DM was understandably mad at the husband. He also told us we should have finished the dive with him.
From my point of view, the DM made three serious mistakes:
1) Not checking the air consumption of divers he knew had limited experience.
2) Sending a diver up alone.
3) Leaving the wife alone on the down line.
This was our last dive of the trip, and we were so shocked we didn't discuss the situation on the way back in. In hind site, I assume he was in a rush to surface to make sure we made it to the boat. If that were the case, he should have gone back down to her once he saw we were OK.
Sorry for the hijack, but I guess the point of my story is that I'm opposed to solo ascents.