It is a hard argument to make that the US dollar would be "dead in 2 weeks" if the Euro fails. The European Nations would be looking for a new currency to depend upon until they get a new national one established, and the dollar is the natural remedy for that case.

On the one hand, it is obvious that the US as a whole would be affected if the Euro died, because the EU is the biggest importer of US goods, so our already declining manufacturing base would suffer, and unemployment could go up while Europe flounders in currency issues. But, as stated above, these nations would need some sort of medium of exchange, and there are lots of dollars floating around and widely accepted.

Still, the Chinese Yuan could fill the void as well. And if it did, and now OPEC is sending more oil to Yuan-based countries (I know, unlikely, but still, work with me here), then the dollar could be dropped as the "petrol dollar" and then we would be screwed. Of course, the dollar is supported by the full might of the US military. So again, unlikely.