The US economy won`t collapse, if there aren`t any gold stored in Fort Knox.
According to Wikipedia:
"As of November 2017, Fort Knox holdings are 4,582 metric tons (147.3 million oz. troy), with a market value of over $100 billion. In contrast, the GDP of the United States was $19.4 trillion as of April 2017."
This year,the US GDP is more than 20.413 trillion USD.
I don`t think that bitcoin popularity will increase ,if the US government has no gold reserves.
Nobody cares about that.People are just ignorant.