Nothing contained in sections 1121 through 1132¹ shall be construed to supersede or preempt a provision of a collective bargaining agreement in effect on July 23, 1970, or on any date subsequent thereto, negotiated by a school entity and an exclusive representative of the employes in accordance with the act of July 23, 1970 (P.L. 563, No. 195), known as the “Public Employe Relations Act,”² which agreement provides for the right of the exclusive representative to grieve and arbitrate the validity of a professional employe's termination for just cause or for the causes set forth in section 1122³ of this act; however, no agreement shall prohibit the right of a professional employe from exercising his or her rights under the provisions of this act except as herein provided. However, if within ten (10) days after the receipt of the detailed written statement and notice as required by section 1127,⁴ the professional employe chooses to exercise his or her right to a hearing, any provision of the collective bargaining agreement relative to the right of the exclusive representative to grieve or arbitrate the termination of such professional employe shall be void. Professional employes shall have the right to file a grievance under the collective bargaining agreement or request a hearing pursuant to section 1121 through 1132, but not both.