We did an excursion in St. Thomas with a lady who said she got off the boat in Tortola with her 2 daughters, found a taxi and just kind of went on a tour of the island and then to the beach for a little bit.
We didn't have anything planned for Tortola so got off, walked through the approximately 5 shops that are currently open at the Pier Park and got right back on the ship. We're not really the type to just get in a taxi and go but it seemed to work out well for her. I did enjoy having time on the boat with fewer people but Tortola seemed very safe to me based on the limited time we were there.