What happens if
Leopold Clement, the Prince of Lorraine did not die in 1723 to smallpox?
He probably married Maria Theresa instead of his brother and the House of Habsburg-Lorraine still comes into being. But there is a greater chance Francis marries someone else and either fights for Lorraine (which he wanted to do in OTL) or becomes the resident Grand Duke of Tuscany (which he never was in OTL).