Company is not fiction to believe in, it is an agreement a contract by the society encoded in a set of laws. The laws governing companies, unlike the market-value of assets, are very resistant to change. Market values change very often, especially values of crypto-currencies. Laws don't change often.

A company exists and has valid standing not because people believe in it but because the law says it exists. It is easy to prove beyond reasonable doubt that a company exists (or not). That has nothing to do with whether people believe it is valuable.