- pay the salaries of state workers
- pay your tax
It may not look like much, but it's the reason why a regular currency is always worth at least something : some people are legally bound to using it.
There are many fiat currencies that went to zero and no longer exist. Most recently is the Zimbabwe dollar which ceased to exist some years ago and the country had to start using USD and ZAR.
pay the salaries of state workers
When the fiat currency collapses like in Zimbabwe, state workers no longer accept salaries in the currency and demand something else.
And also, when I say one person buy it for a million in actuality the probable “floor value” scenario is a million speculators trying to buy it for a billion dollars.
Bitcoin has been unleashed on the world and it will forever have a life of its own. Unless, of course, enough governments ban it and enough citizens obey the ban. Eventually even this scenario will become impossible.
I mean, one person buying all the bitcoin would be an excellent way to cause the value to go to zero. If every bitcoin is held by a single person, who else would care?