[office_drone]

You're right that he's rich because he owns part of Amazon. You're not right that a stock price fall would make him not-rich.

The textbook way to price stocks is at the present value of future cash flows. That is, the company does make money, or will in the future, that can be returned to shareholders. Amazon takes in a ton of money, turns a profit, and could return some of that money to Bezos for him to spend. (Whether or not they actually do is a tax law triviality.) It wouldn't matter if the shares were priced at $1 or $1000, they would theoretically return the same cash to Bezos for him to spend, which is why he would still be rich.

[oh_sigh]

He would still be rich, but not as crazy rich. And if he did want to return money to the share holders, it would come at the cost of reducing reinvestment into the company, probably lessening their moat.