It will be your own fault. there is no reason to miss an Alaskan sailing ship. The towns are all walkable back to the ship and scheduling of any independent tours shouldn't end any closer than 2 hours before sailing. At the dock will be a cruise agent - also will be listed in your ship newletter given out the night before. You would contact them, and make costly arrangements to meet up with the ship at the next port. If you "just" miss it- sometimes you can board via a water taxi- again it is unknown if ships accept these passengers any longer due to increased security? Anyone know?