I think, after they left, Kuki must have gone and searched for Chandni below... She must have found Chandni alive and badly hurt and crying for help... But being the witch that she is, she must have left her moaning in misery to die... After some time Chandni must have become unconsious and Kuki must have thought she is dead and she must have left the spot... Later some villager must have found her and saved her life...