I'm a solo bike tourist, except for occasional riding with people I meet along the way, so I may not be the best expert. But I do have an opinion about how this situation could have been handled.
I'd assume the attitude (and encourage the others likewise) that it's not critical to the success of the group overall to ride together. Those that want to ride with others will do so and those that prefer to travel at their own pace (or leave at their own time) will do so as well. Each evening, I'd communicate with the others about the target camping location for the next night. Allow everyone to discuss amongst themselves what time they want to leave in the morning and form groups if they want. Otherwise, I'll see you all at the next camp site. Have a great ride tomorrow!
If someone wants to leave at 10am and ride slowly, no problem. That's your choice. We'll happily see you at the next camp site. If someone wants to leave late AND ride with others, that person should be making those plans with others in advance. No problem. See you at the next camp.
I'd exchange cell phone numbers with everyone for use in case of trouble or an emergency change of plans.