You are not rich until you cash out. Until then you're rich on paper.
Many forget that. And I bet any bitcoin millionaire ain't gonna cash in fiat ever. Spreading it into alts or investing in something else rather than piling up cash
It may be not as simple as it seems
Even if and when you cash out, you are still only paper rich, so to speak. You cash out and receive dollars, euro, or whatever. It is still the same paper, and all paper will burn at the end of days. People who are not going to cash out no matter what and are determined to stay with bitcoins till the end (some dudes here had been claiming exactly that but I haven't heard from them recently) hope that Bitcoin will completely replace fiat eventually and so they will become a new financial elite