OK just a nagging feeling that you are correct, especially if they were early users. Each purchase of Bitcoin with US Fed Notes has a two fold effect. First the Buyer, transfers money out of a US bank account and buys the Bitcoin. Second, the seller takes the US Fed Note and puts it where? Now that is a big question. Did it go into a US bank or an offshore account? Let's assume an offshore account. What does that do to the credit system (think fractional reserve)? If that is what is going on what will happen? 1. Credit system seizes up. 2. Business comes to a grinding halt - unemployment skyrockets.
Desperate to pay the bills and buy essentials all US citizens sell any asset they have - Bitcoin; gold; silver; houses; the stock market all of which tank in price. 3. Those who hold cash offshore buy America at fire sale prices. 4. With America down no more food exports world starves and goes to war. 5. Those who owe the Federal Reserve ie ECB, sell all assets to raise cash. 6. All other nations of the world lose their biggest customer and face a similar situation.