Here is my idea
On 1370, Casimir III decided to be careful about his own life and not to engage himself of things that would be harmful to him like hunting after a bad dream about his own country.
In 1371 Vladislaus of Opole and Casimir III led an armed expedition against the Crown of Bohemia (this assault caused a terrible devastation of Moravia) which led to the treaty of Krakow of 1371 which had the Duchies of Cieszyn, Raciborz, Bytom and Opole to be under Polish Suzerainty as an exchange for peace.
On 1378, after Elisabeth of Pomerania was widowed from the death of Charles IV of Bohemia, she was recalled and she was married to Siemowit IV, an ally of Casimir III.
The Children of Charles IV would have some sibling rivalry and for that reason, Bohemia would be unstable, however they would be unstable and any war between them.
Wenceslaus IV would speak ill of the children of Elisabeth of Pomerania with Charles IV, in this point Siemowit IV would have children of his own with Elisabeth of Pomerania.
How would longer living Casimir III affect the Hussites in Bohemia, how would a longer surviving Casimir III affect the Hussite controversy in Bohemia if it still happens ITTL?