(a) for an employee when he ceases to be employed in the area or occupation for which the differential was authorized; or

(b) for an occupation when the Director of Classification and Compensation, with approval of the Director of the Budget, determines that the substantially higher private or nonstate wage rate in the area where the differential has been paid no longer exists. Employees who on April 1, 1979 are receiving additional compensation, as a result of a previous determination to authorize a geographic area pay differential, shall continue to receive such additional compensation while employed in the position for which such differential was authorized.