I would remind you that I pointed out that central banks are moving slowly and carefully to reduce their dollar holdings because a run on the dollar is not in their interest. An exception might be China if they decided to use it for assymetric warfare, but they would suffer a lot of economic damage, too. The biggest risk of a run on the dollar lies in the billions of dollars out there in private hands, both banked and unbanked. In many countries, bank acounts, CDs, loans, and other products can often be held in a variety of currencies and the dollar is usually one. Local people often held foreign currency accounts, It was not just expats. Even though the local currencies have been stable for a while, the memories of rapid declines are still fresh enough that most local people prefer to keep their savings in hard currencies, the dollar, euro, or Swiss franc., which is why local banks have accounts and CD's in other currencies.
The dollar's value held steady from the 1790s to 1913 and has been gradually declining since. Today's dollar has the purchasing power of aout 4 cents in 1913 money. In my lifetime, it has dropped quite a bit. Today's dollar is worth about what ten cents was when I was in high school. As out national debt mushrooms, it is not going to get any better. If we can knock down the national debt, our inflation problems can be whittled down, but that is going to be tough to accomplish.
The loss of value varies among fiat currencies, some better than the dollar and some worse. The currencies that merged into the euro are now hard to compare, but using two that did not go into the euro illustrates the point. When I was in high school, the British pound was $2.80 and the Swiss franc was 23 cents. Now the pound and the Swiss franc are worth a little more than a dollar. The Swiss franc held its value much better than the dollar and the British pound much worse.