HRE Josef II had only one child by his beloved first-wife, Maria Theresia Elisabeth ("Titi"), born in 1762. Now, Titi died young of smallpox (I think) in 1770. By then, Josef had been married again and widowered again, so I think it's fairly safe to say that Titi would be his only surviving child. Meaning that while she couldn't be elected Holy Roman Emperor, her husband could.
So, what if Titi were to survive? What might the future look like for her? And Europe?