1241 is doing a lot of heavy lifting in this whole what if game, huh? Everyone acts like Vienna was saved by one guy dying at the exact right moment, like Europe had some magic shield that Ogedei's death activated. The Mongols did smash stone walls at Kiev and Baghdad, sure, but they also lost guys to Hungarian castles at that same time, so it's not like they were unbeatable. Maybe the bigger thing was they were already stretched thin after riding halfway across the world, and Europe is basically one big wet forest full of angry dudes in armor. A dead khan is a convenient excuse, but armies run out of steam for boring reasons too.