Section 9(10)(b) in The Maharashtra Employees of Private Schools (Conditions of Service) Rules, 1981
(b)In case it is not possible to fill in the post of a Head or Assistant Head for which a vacancy is reserved for a person belonging to the Castes and Tribes specified in clause (a), the post may be filled in by promoting a candidate from the other remaining categories in the order specified in clause (a), so however that the percentage of filling up such vacancies does not exceed the limit laid down for each such category. If candidates belonging to any of these categories are not available, then the vacancy or vacancies -(i)of the Head may be filled in by promoting any other teacher on the basis of seniority-cum-merit after obtaining previous approval of the Education Officer;(ii)of the Assistant Head shall be kept unfilled for a period of three years unless such vacancy or vacancies could be filled in by promotion of any teachers belonging to such Castes or Tribes becoming available during that period.