If you get left behind in port, you are responsible for your own transportation to the next port or back home. The costs can be several thousand dollars each and will be even more complicated if you are traveling without a passport.
Our advice? Plan on arriving back near the ship 1 1/2 to 2 hours before you are scheduled to leave. This not only gives you some time to shop in the port area, but also gives you plenty of leeway if you run into traffic or your taxi or bus has a breakdown on the way back.