I like to guess how things might have turned out if the Balkans never came under Ottoman rule. So, here I go.
The three core Balkan powers (Serbian, Bulgarian and Byzantine Empires) would have probably stayed powerful up to this day. The rise of the Austrian Empire would have probably never happened too since a lot of it was dependent on taking large portions of Balkan territories and Hungary. The Magyars would've probably ended up taking all of Austria and Magyarizing the area.