Countries hold reserve currency to pay debts and avoid the balance of payment crisis. The reserve currency can be used in such cases as it is a safe-haven currency.
How Did The U.S. Dollar Become The Reserve CurrencyThe United States has been a lucky beneficiary of the two World Wars. It was geographically far away from the actual destruction happening to various countries in both the World Wars.
The U.S. dollar losing its reserve currency would necessitate another currency to take its place. At this time, no other country’s currency provides stability, convertibility, and wide spread availability as the U.S. dollar.