In OTL, the Jageillion dynasty through the male line went extinct in 1569 when Sigismund August of Poland died without heirs. Now, in OTL there was also the second branch of Jagiellons who ruled Bohemia and Hungary. Their line male line went extinct in 1526 when Louis II of Hungary died at Mohacs, which allowed the Hapsburgs to lay claim to the Kingdoms of Bohemia and Hungary.
Both Louis II of Hungary, and Sigismund Ausgust of Poland were the grandsons of Casimir IV of Poland.
So what if Louis II doesn't die at Mohacs and is able to survive. Also, lets assume that Louis achieves a rather decent age (the Jagiellions were a rather long lived lot) and is able to at least briefly inherit Poland and Lithuania upon the death of his cousing before passing it on to his ATL son.
For the sake of discussion, lets assume that Louis's descendants are able to hold on to the three kingdoms and the Grand Duchy for a while.
How do things turn out with a King who rules Bohemia, Hungary, Poland, and Lithuania?
Might we see come kind of analogue Union of Lublin? In OTL, Lithuania was pretty opposed to joining with Poland, and they might only remain in personal union in this TL... but with Hungary in a weakened state, could we maybe see some kind of union between Poland and Hungary (and maybe Bohemia)?