Loss of reserve currency status is happening regardless of the Iran deal.
With yesterday's devaluation of the yuan, that doesn't look like a safe bet to replace the dollar as some pundits like Zero Hedge thought.
As an aside, just last month Russia's Gazprom agreed to deliver oil to China in exchange for yuan. As a result of yesterday's devaluation, Gazprom just took a 2% haircut based on exchange rates alone.