In the spirit of Accident Analysis, here's my take based upon things in the official record and second hand information I have heard on island...
1. The Cayman Aggressor was moored in an area where it could not fit through the boat channel to reach a nearby dock. It was a site quite far from where public rescue resources are based. Fortunately Ocean Frontiers had a boat nearby and was able to render assistance. What would have happened had that not been the case?
I would recommend that the Aggressor have a tender in the water when dives are conducted at such sites and that their staff is trained on the procedures to dock that tender at the nearest dock. (proper approach through boat channels, areas of coral heads to avoid, etc....)
2. Local word from another boat captain on the water that day is that the Cayman Aggressor hailed the OF boat via VHF radio and then switched from channel 16 to channel 18 to discuss the missing diver.
VHF channel 16 is the designated emergency frequency for short range marine use. That is the channel that emergency response agencies will monitor. Switching channels is a habit for normal everyday communications but MUST NOT happen in a true emergency unless directed to do so by an emergency response agency. Timely notification of emergency response is imperative. Use VHF 16 or simply dial 9-1-1. The site was very close to shore and cell signals easily reach. Cayman has a police helicopter that could have been overhead in 5 minutes to assist in any search, if the chopper was available.
3. There are certain allegations about the diver's behavior during prior dives. The exact statements are not important and may not be true, but lead me to simply reinforce that making a safe dive plan and sticking to it are of the utmost importance. Get your health checked by a doctor before a major dive trip, especially if you are of advanced age. Practice healthy hydration during a dive trip. Go over the depth and time with your buddy and STICK TO IT. Stick to your MOD for your nitrox blend. Plan communication signals in advance.