"Where: (a) an employee has the right conferred by section 79, and (b) it is not practicable by reason of redundancy for the employer to permit her to return in accordance with that right, and (c) no offer is made of such alternative employment as is referred to in section 81, the dismissal of the employee which is treated as taking place by virtue of section 96 is to be regarded for the purposes of this Part is unfair."