You're suggesting that on a dive charter there are only two divers (or nobody else has a reg) and there is no spare reg on board. That does NOT sound like a typical charter to me.
Also, you're suggesting that there is wreck penetration occurring with recreational-only divers (no longhose) diving with no safety bottles, and in an area where you can slide a 7" diameter tank but not a person or a reg? Seriously, at what point does Thor tell Zeus to release the Kraken?
You forgot to mention that the new tank arrives just as the diver has finished off the old one, so he does not have time to switch any equipment.
---------- Post added November 6th, 2014 at 02:34 PM ----------
To give you idea about what it takes to switch regulators, let me describe an experience I once had.
I was diving in Cozumel when the DM had an explosion of air from his first stage. I got to him in seconds as he pulled off his BCD and swung it around in front of him. I saw him shut off his air, so I offered an alternate. He didn't take it. He opened up the regulator first stage and saw that the O ring was extruded. He replaced it, which took a while. He was just about to complete the reassembly when he decided to take a single hit from my alternate. He then finished reassembling the first stage and went back to breathing from his own regulator. It took him a little more than one comfortable breath. He could have done without my help, but it would not have been comfortable.