The USD is the world's reserve currency because its instantly convertible to any other currency. Nothing is actually paid for in dollars, its paid for in "euro-dollars" which is a weird contract term that simply means a contract written where the standard unit of exchange is in dollar terms. No dollars actually change hands.
If I am in China and wish to by Oil from Saudi, I go to a bank which does the exchange rate from Yuan to Dollars then Riyal to dollars, then does the math and tells everyone how much to pay. And takes their cut. The dollars get stored at the respective countries central banks. No dollars actually changed hands between the private parties.
There now skipping the bank. The Central bank will need to hold less dollars, so that is important. But no one wants to hold Yuan or Riyal either. So that has not changed.
The US dollar will die over time like all Fiat currencies, but its self induced.