What matters is if the nations sell in Euro then all the importers dump the dollar to buy Euros. Euro value goes up, but the dollar might easily start a death spiral with our credit along for the ride, while the interest rates shoot up faster then the magic bean stock.
Then,....we'll have to create a 'Homeland Security Force' to keep law and order?
/sarcasm?
Right. And this seems to be what is happening, Saddam wanted to price his barrels in euros: the europeans loved him, the US invaded and captured him. Now the russians are pricing their oil in euros, however you cut it up, it looks like a freefall for the dollar. The only good thing, weirdly, is that our dollar is pegged to the chinese currency, so imports from china won't increase that much if the dollar continues to fall, keeping inflation in check.