I'll just talk financially for the US.
The US has never reached a critical or super-critical population mass (in terms of the workforce).
If all Black people left, it would create an immediate, extreme recession.
Also, like any capitalist society, the US thrives on consumerism, which is something that black people take heavy part in.
Without black dollars flowing to these companies, you will see them shut down in days. I mean look at how many companies have gone belly-up in covid.
Actual economics fly in the face of those who fearmonger that the US has reached a critical mass. If the US were to suddenly lose such a signaficant percentage of workers, taxpayers, homeowners, business owners, debt holders (that matters too). the result would be catastrophic.