"So now comes the issue of what happens when demand for $US drops? How could this happen? Well, that oil previously sold for $US is now sold to China, and numerous other countries for something other than $US, and countries like Russia, Syria and Iran are producing oil not sold in $US that the country issuing $US would very much desire to be sold in $US to keep inflation down at home."

The oil priced in dollars is just a unit of account, it doesn't really determine the value of that dollar.

What ultimately determines the demand for dollars is not the unit of account for the transaction, but rather the desired asset holdings of those who are accumulating the wealth.