It's very, very difficult to picture doing this and, before I did it, I swore I would never do it! LOL! Our DD13 at the time swore up and down she would go with us very willingly with a good attitude to Stingray City and Coral Garden. We had hired a private boat and captain and the whole deal. Well, once we were on the ship and she was having a blast with friends in Edge, she begged us to let her stay on the ship and not go on the excursion. We just couldn't do it and insisted she come along. She made that trip miserable for the rest of us with her poor attitude, saying she was sick, complaining, on and on and on. This was a once in a lifetime event for us and she soured it greatly.
The next day was Cozumel and we wanted to snorkel again. DD didn't even have to ask if she could stay on the ship, I asked her first if she wanted to stay in Edge while we were off and she, of course, agreed. I spoke to the CMs and told them I was nervous leaving her on the ship while we were off in a foreign land. The CM assured me all would be well and it was. We were gone for about 2.5 hours.
I don't think I could leave my little ones on the ship without me, but it worked out fine with our teen and I would do it again. Before I sailed I wouldn't think it would be a good situation at all -- my mind can go to some awful places. But once I was onboard and saw how it all worked with the club, I was fine.
If you don't go on an excursion, I hope you will at least get some adult time together on the ship. It's your vacation, too!