Don't forget about the numbers who are employed by healthcare providers to navigate the many policies and companies so they can get paid. Some economists I know suggest that the total unemployment resulting from single-payer could reach a million in the US.

That, along with direct cost control savings, would make it a "deflationary" event that would require a considerable injection of public money to mitigate. If we got it wrong and approached it as "inflationary", attempting to pay for it via taxation or fees, we could do serious damage to the economy.