What do you mean “now what?” lol. Assuming an American-centric or Euro-centric point of view, they would use their extremely expensive military armaments that can’t be purchased in large quantities by private organizations, and crush the rebellion. The government is the government because they have a monopoly on violence.

I mean, really. Their money is in banks subject to the oversight of the countries they’re trying to raise an army against. People may be relatively cheap, but they still need to be paid quite a bit to attempt to fight the military head on. Freeze their accounts and they’re screwed. Musk’s entire fortune isn’t even a single years worth of funding for the US military, and even if all the billionaires pooled their money it would take years to accumulate the excess hardware that is allowed to be sold and then train their PMCs on hardware. Years that they wouldn’t have if a bill was passed to cap wealth inequality.

We may yet reach the corporate dystopia where businesses can directly challenge governments, but we’re not quite there yet. At least not in the first world. Russia may have shot itself in its confusion, but that’s because the rich already are the government there.