I believe Hitler specified a sort of racial hierarchy. Some ethnic groups would be kept as a slave class, not educated at all so they would just be a manual labour force.

Hard to imagine what Hitler would have done, but I cant see them wasting the resources available by keeping a working class in Russia. At least not for a long time until a larger German population could do it themselves.

If the Nazis really needed labour from Jews, Gypsies, and Poles then they might not have been murdered so soon either.