Really? Poland get 12billion Euros per year from the EU. Paid for by Germany, the UK and the Netherlands.
At the moment, the Euro makes German exports artificially cheap. As German wages are relatively low, despite the high know-how behind its products, German wares have a competitive advantage. As soon as the Euro is gone, the new German currency will rise in value, while the Polish Złoty will be depreciated. This means that, at this point, German wares will be too expensive, while Poland will not be able to afford any imports from Germany anymore. The German economy will see a massive downturn, probably a collapse of some firms, and a steep rise in unemployment.
As an additional problem, the end of the Euro will probably not come in an ordered fashion, but quite suddenly. At that moment, much of the trade surplus of Germany and the loans given, which both are counted as assets nowadays, will have to be written down as a loss. This means that the means of the government to compensate for the economic downturn will be very limited in such an event.
Long-term prospects are different, but the general level of the economy will be lower than today. Germany's prospects are not very good anyway, as it has structural deficits in its economic branches.