What if Frederick Christian never got smallpox and was elected King of Poland while being the Elector of Saxony, keeping the Union of Poland and Saxony intact?

The personal union between Poland and Saxony, known as the Saxon period, lasted from 1697 to 1763. This union began with the election of Frederick Augustus I, Prince of Saxony, as King of Poland (Augustus the Strong). The union aimed to bring about a far-reaching unification of the Polish-Lithuanian Commonwealth and the Electorate of Saxony.

Frederick Christian, son of Augustus III (King of Poland and Elector of Saxony), was the last leader of the Union of Poland and Saxony. He contracted smallpox shortly after his father's death. Due to his illness, the electors decided he wasn't a suitable candidate for the Polish throne (He also was already a bit sickly). Although he became Elector of Saxony, his reign was tragically short, lasting only 73 days before his untimely death.

After Augustus III's death, the Polish throne passed to Stanisław Augustus (Stanisław Poniatowski). He was the ex-lover of Catherine the Great of Russia, and with her support, he ascended to the throne. Despite his progressive reforms, including the Constitution of May 3, 1791, Stanisław faced immense pressure from neighboring powers. This ultimately led to the partitions of Poland in 1772, 1793, and 1795, and the eventual dissolution of the Polish-Lithuanian Commonwealth.

Frederick Christian was a reformist and enlightenment thinker, he said thing's such as "Princes exist for their subjects, not subjects for their princes. His subjects' wealth, public credit and a well-standing army make up the true happiness of a prince. This is the link to his Wikipedia page: https://en.m.wikipedia.org/wiki/Frederick_Christian,_Elector_of_Saxony

But what if Frederick Christian hadn't contracted smallpox (while also not being sickly) and was deemed fit to be made King of Poland, keeping the Union of Poland and Saxony intact? How would a leader free from Russian influence have shaped Poland's future? Furthermore, how might Poland owning Saxony have impacted events like the Napoleonic restructuring of the Holy Roman Empire into the German Confederation and the later unification of Germany? Could Poland have united Germany under Saxony or at least become a major player like Prussia or Austria?