This hypothetical assumes dollars do not remain legal tender - at least in the sense that people would not be willing to offer credit denominated in dollars. C

This hypothetical assumes dollars do not remain legal tender - at least in the sense that people would not be willing to offer credit denominated in dollars. Currencies have pretty strong network effects - there's a strong incentive to use the one most widely accepted, because you can then spend it in the most places, assuming free trade and common markets. That's why national currencies like the deutschhmark and lira have largely been replaced by the euro. Or, for that matter, why BCH, BSV, and ETC are virtually worthless while Bitcoin and Ethereum's value has skyrocketed.