Billionaires purchase very little consumption, as a fraction of their wealth. Most of their wealth is invested. So if they locked up their money in a vault Scro

Billionaires purchase very little consumption, as a fraction of their wealth. Most of their wealth is invested. So if they locked up their money in a vault Scrooge McDuck style, what would happen is that interest rates would rise, and asset prices would fall. Whether that's good or bad depends on whether you are a borrower (bad) or lender (good). Everyone is a little bit of both (e.g. they have some retirement investments but also take out mortgages and auto loans), so there isn't a simple answer to the thought experiment. And this also changes based on the government policy, as this thought experiment assumes no government. Government could react in a number of ways, from buying bonds directly to offset the wealthy selling their investments, or raising interest rates, or increasing public investment, depending on whether the government is more interested in price stability or maintaining total investment, or some other objective. The main problem is that you are assuming that a group of people, en masse, will begin to act irrationally, and that's generally not how we think of economic interventions, but it's a good exercise to do.