A Judge may be permitted to combine vacation on full salary with leave, if―
         (a) where the vacation consists of one continuous period, the leave is taken either at the commencement or at the end of the vacation but not at both;
         (b) where the vacation is divided into two periods, the leave is taken for the interval, or part of the interval, between the two periods of that vacation, or for the interval, or part of the interval, between the second period of that vacation and the commencement of the next ensuing vacation:
     Provided that no such permission to combine vacation with leave shall be granted, if it becomes necessary to appoint an acting Chief Justice during the period of vacation or if the Judge is not expected to return to duty at the end of such leave.