There is simpler way to make Jagiellons lasts longer, IOTL dynasty was possibly doomed by idiotic show organized by Sigismund I in forests near Cracow in 1527-he ordered to release big bear caught in Lithuania from box, then hunters would kill him during hunting party. Bear was initially sluggish, but once he was out of the box, instead to run into forest, he attacked hunters and caused panic among spectators watching the hunt. Pregnant Queen Bona was among them, she watched the show from horseback. Her horse was scared and she fell. She gave birth to premature child-son, who lived only long enough to be baptised as Olbracht. So to save House of Jagiellon just prevent this hunting accident.