There is zero chance that Germany will go back to the Mark.
Ireland and Greece are tiny countries. Their problems are totally blown out of proportion. Germany has a GDP of around 2.5 Trillion Euro. The EU has a GDP of 12 Trillion Euro. Ireland has a GDP of around 160 Billion.
The Euro being under pressure? How is that bad news for Germany's export oriented economy? It is not.
Second, the countries like Greece and Ireland under pressure? That's also great for the greater EU. It makes everyone aware that changes in economic policy are needed. Up until now in many areas the EU and Eurozone countries have different economic policies that are not really adjusted to each other. There is now some chance that this will change.
The internal problems in Europe have been caused by a few factors:
* the banking system took a lot of risks and also invented fancy new products (aka ponzi schemes)
* bubbles in a few countries, especially the housing bubble in the UK, Ireland, ...
* budget deficits for example in Greece, UK, ...
The financial crisis has exposed these problems. Giving up the Euro does not solve any of these problems.
The single currency market of the Eurozone has been given such a boost to the economy that very few people would be willing to give that up. The only real question that is worth discussion is how to repair the broken parts.
All other speculation in this area is wishful thinking and market manipulation from people who want to profit from the manipulations.