User blog comment:AnonymousAK/Demon's Royale/@comment-25121709-20140715151833/@comment-24800928-20140715210414

zoldeo can only be forced out a body by two reason 1) he chooses to leave the host 2) a specific spell (like Regulus) is used to expel him out the body

The removing of the key from Lucy is not valid because in this case we are working with something completely and utterly non-canonical. This is all hypothetical and therefore we are focusing on the Zoldeo-possessed Capricorn ie one of the members of the seven kin.