That is a fundamental misunderstanding among the tinfoil hat crowd on this site.
USD is worth something because ultimately it's backed by an army that can insist you pay your property tax in USD, and because it's backed by the outflow of payments from the US government, which only pays its people and contractors in USD.
No way. The USD wouldn't have its value if China didn't approve it. This is because USD is currently the world reserve currency. U.S. army would not be able to invade China, because China has nuclear weapons. U.S. has 17 trillions of debt and if the creditors (for which China is one) wouldn't approve USD then U.S. will default, USD will collapse and U.S. gov would not be able to finance its army and therefore it wouldn't be able to protect its own nation, and then riots everywhere and the society collapses along with the USD.