What I think is that Celestia and Luna are still going to raise the sun and moon, because Twilight doesn''t have those powers. Luna will also continue to dreamvisit, so Twilight won't have to worry about that either. As for the School of Friendship, I think the Young 6 will run the school now, cause probably Starlight Glimmer will move to Canterlot also.
Oh yeah, did I forget to mention my Princess Starlight Glimmer theory?