You think Europe would've been home to countless millions Africans and Arabs had Hitler won?
We'd probably be mining the moons of Saturn today had the Nazis prevailed.
Nazi Europe would have been subject to decay like every other society. It might have taken a different form, but they were unlikely to remain dynamic and advancing for 3-4 generations.
And would a slave society, like Hitler’s empire, really have opposed importing foreign labor, so long as it was kept under tight control?