If this aweful (!) thing should come to pass, producers will have excess euro's to sell, not excess dollars. No net effect on the dollar vs the euro, because the lower consumer demand for dollars is exactly offset by the lower producer supply of dollars.
moreover, if anyone wants to buy oil in euros or zlottys or cowpies, they can. find a seller who wants cowpies or a bank that will cowpies for dollars, and you are in business.
What he brought up though, was interesting.
What if these countries just decided to dump dollars?
What if they DID decide to purchase oil with Euros?
While their costs might be higher due to exchange rates, Their decision to go off the dollar and create their own trading block financially IS a de-stabilizer.
The dollar is not a necessity to purchase anything anymore, especialy with an Iranian oil source that can only be closed through an act of war ourselves.
It is the response to this that would prove interesting, for if their little trading bloc took wings, slowly but openly, inflation a divestment in the US due to investors losses based on inflation would be an act of war.