21. Where, because of an interruption or cessation of work at an employee’s place of employment, existing on the date specified in section 20(3) or existing at the time of the expiration of a period of parent’s leave taken by an employee, it is unreasonable to expect the employee to return to work on such expiration, the employee may return to work instead when work resumes at the place of employment after the interruption or cessation, or as soon as reasonably practicable after such resumption.