There is a scene in a later book where a princess, who possesses several severed heads which she can wear as her own head and exchange at will, wants to chop off Dorothy's head to add to her collection (but it's alright, she offers her one of her 'less fashionable heads' in return) The character,a long with the witch Momby was the basis of the villain in Disney's "return to Oz"
And it was also later established (I don't know whether that was by Baum or one of his successors) that nothing in Oz can truly die. So when the Tin Woodsman started to accidentally chop off his own body parts (and had them one of the other replaced by tin) continued to live and some witch assembled them into a new person.
The books have many dark and macabre elements.
In theory that also means the molten Witch of the West and the crushed Witch of the East migth still be "alive" in some way...