We know in world war 2 it was the German's aims to conquer the world and mercilessly murder anything that wasn't a pure German, and resettle the whole world with pure Germans when they're all that's left of humanity.

So let's say they succeeded, they conquered the whole world and murdered every single non German then among the pure Germans they killed everyone except those with blonde hair and blue eyes and then resettled them throughout the whole world what would happen?

Would humanity be to inbred to survive after a couple of generations and become impotent? Would this blonde German world be able to continue forever? Would the bottlenecking of humanity lead German world down a path of inbred deformed humans mutating into horrors? What would happen with a species so culled and so sparse?