That, and past a certain point, 'Catholic' and 'Protestant' become less important than 'German'.If Austria loses its empire, which despite what people claim is by no means a given, there is just too much internal pressure for unification in both Austria and Germany. No matter what concerns or fears anyone might have they would be essentially throwing away any and all power and influence they have by opposing it.
That said, I do think the Habsburgs would remain an international dynasty, much like the Hohenzollerns. The Hohenzollerns, after all, have the main branch ruling as Kings of Prussia and German Emperors, but a branch line also rules as Kings of Romania. I can thus see the main Habsburg(-Lorraine) branch continuing to reign as Archdukes of Austria as part of the greater German Empire, but branch lines possibly reigning as Grand Dukes of Lothringen (also as part of the greater German Empire), as well as Kings of Bohemia and Croatia (i.e. the pro-Habsburg core territory of their former empire).