Also be aware that if there are "issues" with a person being able to enter the US (or re-enter in this case), then the US government will know about it before you get on the cruise. The cruise line submits the passenger manifest to whatever government agency (INS, DHS etc) a week or so before the cruise (or earlier). They may let you board or may not, but they may deny entry at the end of the cruise. This is the main reason why cruise lines can't offer any more of those cool walk-up sales like they used to to fill a ship.