He'd still have a lot of property to his name, a lot of other assets and stuff that aren't tied to an arbitrary stock market. Even if you crash it, mansions and luxury cars would still be very valuable. He will never not be a billionaire due to that.
That is, unless you redistribute his wealth. Then yeah, he wouldn't be filthy rich anymore.
Not an American, but yikes does this have "Vote with us... Or else!" vibes.
That's not to say I support Trump, but I personally don't think this is the way to convince fence-sitters at all.