As for millions of workers leaving the country, that is doable and has been done before. Nearly four million men were pulled out of the economy in 1942 alone, and that when the population was only about 130 million. The economy did not implode. What shortages there were were due mostly to rationing food, fuels and other raw materials to the war effort.
The market could adjust to large numbers of illegals leaving the economy. But, again, your point about government disincentives for work is well taken -- and much more easily solved than our immigration problem.
I think the necessity will have to come back first...and I think you under estimate the barriers to that. I think it’s much worse than you are thinking it is.
I also think you under estimate the many many things that are different between now and 1942 - but I enjoy the give and take...and exchange of ideas.