Caught some of this going on at the start of the war. Kind of silly.
History shows that a reserve currency like the dollar craps out when it loses its reserve status, as a result of things like the deep indebtedness cited above, for instance. At that point the reserves held in that currency have to be sold gracefully, somehow. In 1968, an agreement was reached among members of the British Commonwealth still holding sterling as a reserve to sell it only by agreement among all. In 1999, the Washington Agreement was reached to sell off dead holdings of gold at an agreed-upon rate.
There is currently no good contender to the dollar as a reserve currency. No doubt something will come along someday, but Iran won't be the one deciding which currency gets to be next. That would be, well, absurd, given their insignificance in the global trading order. That decision will lie with those with true trading clout: the Eurozone, Japan, China. Shoot, Dubai has more of a chance of participating in this decision than Iran, if their efforts at diversifying work out.

Another point. A lot of these petro-euro stories hinge on the misconception that a weaker dollar is worse for America. A weaker dollar not only makes American exports more competitive, thus providing a much-needed economic stimulus, but it also makes all that dollar-denominated debt worth less, relative to other currencies. So if the dollar tanks, the US gets its debt slashed straight out and a nice little pick-me-up to get going again. Hardly the doom and gloom scenario that eejits like Pilger would like to portray.