As the title says, WI King Wladyslaw III of Poland and Hungary survives the battle of Varna, what you be the long term consequences for these kingdoms? For the sake of convenience, suppose that the "Crusaders" either don't suffer such a catastrophic loss, or even a victory, but if this POD is not enough, just pick another.
What are the chances of this dynastic union evolving into a long lasting (multiple generation) realm, like the Kalmar Union (or, better, the Denmark-Norway one)?
Wladyslaw III was very young when he died, so we can imagine that he might have sons. As long as the Ottoman threat looms over in the Balkans, I suppose that the Hungarian nobility will support a continued union with their stronger neighbor Poland - they were the ones that invited Wladyslaw to Hungary, in first place -, even more if the successive Polish monarchs continue to use the "championship" against the Turks as an ideological tool to legitimize their rule.
Now, in the long run, how would this arrangement be done? Would the "Rzeczpospolita" model rise in the same conditions, and could it be adapted to include the Hungarians (Slovakians, Vlachs, Croatians, etc), or would it likely remain as a post-feudal Early Modern monarchy? Any thoughts?