Police, military, tax offices are NOT assets that can be liquidated.
The US can cede high-value land, lease ports, etc. to back the US dollar with something physical. The US dollar is not backed by a metal, that much is true. However, it is backed by the entire US now.
Blockchain is essentially a huge, decentralized database (or ledger) that says who owns what. The big issue with crypto is you can manipulate who owns what if you own a majority of the coin available. The other big issue is that nobody accepts bitcoin. Therefore, people are using exchanges and getting absolutely fucked by malicious smart contracts.
You keep talking about the fall of fiat, but you fail to prove that crypto is a valid replacement