If you rotate away from a sim in the late afternoon on the very last day of the term they won't have to re-enroll until you rotate back to them (so can stay in the dorms) and they will still get the grade that you actually earned while playing them for the term that is just ending. I rotate between 7 households and I rotate once per week, so I'm rotating on the last day of a term for my Uni students all the time. It works fine.
Keep in mind also that a term is actually only 5 days, not 7, so you can always feel free to rotate away on any weekend within the term, from Friday night until early Monday morning if you need to.