This is a topic in itself. They have many economists working for them so they might have a contingency plan. The Nixon Shock was a radical shift from the Bretton Woods economic system in which USD was pegged to gold reserves, to control inflation in the 1970s.
USA still have largest reserves of gold bricks in its vaults (i.e. bullion depository).
A multitude of options, from burying in the backyard to posh steel-lined vaults.
www.nytimes.com
The United States Bullion Depository at Fort Knox, Kentucky stores precious metal bullion reserves for the United States.
www.usmint.gov
Beginning in 2010, central banks around the world turned from being net sellers of gold to net buyers of gold. Central banks around the world bought 272.9 tonnes of bullion in 2020.
www.usfunds.com
There were unpublished calls from within USA to let the chain-of-collapses in the banking system continue unabated in 2008* (mischievous as it may sound) but Obama administration felt otherwise and chose quantitative easing.
obamawhitehouse.archives.gov
Central banks may not have the tools to act decisively in the case of another downturn, argues Kenneth Rogoff.
www.weforum.org
Actually, with a gold standard system, it is likely that the Fed could have been much less involved in 2008.
www.forbes.com
Long confined to the political fringes, the movement to return the US to the gold standard is gaining momentum.
qz.com
One may not know what is the next contingency plan.
*There are some who subscribe to following philosophy:
"Hum Tu Dobay Hain Sanam, Tum Ko Bhi Le Dobein Gein."