If the Bundesverfassungsgericht rules that the bailouts are unconstitutional then a new EU treaty will be required. If it rules that the bailouts themselves are inherently unconstitutional then it could rule that Germany has to leave the EU.
In all likelihood the Court will capitulate like they did when they reviewed the Lisbon Treaty first time round but I bet they can hear the squeaking bottoms in Brussels all the way up in Karlsruhe.