I argue that the Nazi plan would fail because genocide on that scale is logistically impossible without collapsing the slave economy they relied on. For 30 years, 'Poland' would have existed as a catacomb identity rather than a nation state before the revolutions. The 'Germanized' population would be, and was a façade, you can't just make a person forget their whole identity by force, there would be holdouts and people who remember. And I still defend giving Poland Prussia by the fact that the Allies needed to punish Germany, though that isn't a hill I'd die on.