Post by Graham TruesdaleIf https://en.wikipedia.org/wiki/John,_Prince_of_Asturias had lived and produced offspring, he and they would have inherited Spain, Naples, Sicily and Sardinia. But in this scenario, Philip the Handsome (Habsburg) still inherits Burgundy from his mother as well as Austria from his father. To avoid this, you would probably have to prevent either his parents' marriage or the birth of a son. And that would get rid of Philip's son Ferdinand, who married into Hungary.
Indeed, the whole set of marriage inheritances as we knew them would be disrupted, and the Habsburgs would just be measly little Holy Roman Emperors, Archdukes of Austria and ruler of the scattered southwest German holdings called "Hither Austria".
However, since the Habsburgs in several generations intermarried with Bohemian and Hungarian royalty, perhaps a generation later things could work out so that the Habsburgs inherit the Crowns of Bohemia and Hungary. I think the Habsburgs tried for marriages more often with those neighbors than more distant lands' rulers, and often Bohemian or Hungarian rulers themselves had been interested in expansion into Austria.