Fridge Brilliance: Why was the Witch of the East not brought back? Because Witches have to realize they can be killed in order to possess another. Dorothy's house killed the Witch of the East so quickly she didn't know what hit her.
Fridge Horror: Why didn't the Witch of the South do anything to save the Munchkins? The Munchkins were supposedly under the care of Glenda and she did a better job of keeping them from the Witch of the West. Unless the Witch of the South had no jurisdiction to defend the land of the Munchkin or if she wasn't strong enough to fight the Witch of the West, there's no reason why she wouldn't have been able to save the Munchkins from total annihilation.