He might end up waiting as long as Anna Maria Luisa de Medici to be married. And considering how many failed betrothals she went through - Savoy, Modena, France & Portugal - Gian Gastone (call her Margherita Vittoria) might end up as a spinster caretaker for their father. Although it might be fun to see the reaction to her homosexual proclivities if she's the same as her OTL counterpart. A good match for her might be Cardinal Francesco Maria when it becomes apparent that the Medici are dying out - although by then she might be too old