I've never known anyone who missed the ship, but we have almost missed the ship twice. The 1st time we were in St. Kitts on a Carnival excursion and our driver simply stayed to long driving around the island showing us special things. I think we got back to the ship about 5 minutes before the ship was to set sail.
That was back in 2001 when we were on the Holiday and before S&S cards, so I don't remember how they accounted for who was on the ship and who wasn't.
The last time was in 2007 on the Freedom in Naples. We had a private tour along the Amalfi coast and Pompeii and the traffic is so bad in Italy that I was sure we were either going to miss the ship or be in a bad wreck on the way back. They drive so crazy I had to stare at the floor the whole time there were so many close calls. We got back with only about 15 minutes to spare. My sister was sick that day and had stayed on the ship and knew I wasn't back yet. She was worried sick about whether to get off with our passports, but just as she was about to go to the cabin, she saw me coming out of the terminal headed for the gangway.
These days we don't do to many excursions other than maybe a little shopping or relaxing close to the pier in the morning. We prefer the quiet and calm of the ship.
Festival 5/1983, Festivale 6/1984, Holiday 7/2001, Inspiration 2/2002
Paradise 3/2004, Pride 9/2004, Victory 5/2005, Conquest 4/2006
Conquest 9/2006, Freedom 3/2007, Glory 9/2007, Conquest 2/2008
Valor 5/2008, Glory 8/2008 & 9/2008, Fantasy 2/2009
Conquest 9/2009, Dream 12/2009, Conquest 2/2010, Ecstasy 4/2010
Conquest 9/2010, Ecstasy 2/2011, Glory 2/2011, Conquest 10/2011
Triumph 11/2011, Magic 3/2012