I don't think you have to get off the ship. In fact, I remember Kevin and John mentioning they've stayed on the ship and enjoyed the adult pool while most of the guests left the ship. They mentioned it was a great time to rest, relax, and enjoy the pool area.
We had to drag DS off our first cruise when he was 4 1/2. We did a 4 night bcs we weren't sure how he would do w/ the kids clubs, etc. Turns out he loooooved it and he carried on the whole way off the ship crying "I don't want to leave" over and over.
So they CMs have seen it before. They just laughed and kept on waving their big mickey hands.
During our 2004 cruise trip with our friends, we enjoyed staying and we don't have to get off the ship. We are having fun there, really a great relaxation. So you don't have to get off the ship.