While this trip will obviously be a family reunion for Harry, previous reports claim that he and the Queen are in for some ~tense talks~ about his political involvements in America—which apparently the Palace feels is a "a violation" of their agreement.
(To be clear, all Harry did was simply encourage people to vote, which hardly seems like a breach of royal political neutrality? But like...k.).
Either way, a source previously told The Sun that "Staff at Windsor have been told to prepare for the possibility Harry could come back.