Maybe there would have been a semi-autonomous proto-Yugoslavia within the empire? Something to keep the south slavs relatively happy while holding AH together? Or would this just encourage the Czechs to push for more autonomy?
If Serbia has been crushed, I think it would be fairly easy for the Hapsburgs to play the various South Slavs against each other and Bulgaria to prevent any kind of union. There needs to be a strong center of gravity for a Yugoslav entity to develop, and in a CP victory this will not be the case.
I think another big issue is Poland. The Poles were a critical group in maintaining German-Magyar supremacy in the empire, but the Poles supported the Hapsburgs as the lesser of evils. If there is a potential Poland, they will gravitate toward that.
Even without all that, the Czechs will present a problem, but not one that really has any potential to tear apart the empire so long as the army is strong and Germany supportive.
But this all underlines that A-H isn't really a Great Power anymore - it's a junior partner of Germany.