Germany has been pretty slow till now implementing the JAR, but they are not alone there. Maybe they looked at their neighbours, the Netherlands, and decided not to jump at it, but to take a little more time?
Latest news I heard, they are still busy implementing, only the starting date is moved every time and time again. It seems unlogical if they would withdraw now, because the integration of the JARs already is taking place.
To withdraw at this point would almost be as stupid as the UK not joining the Euro
Greetz