Legal remedy against possibility of defamation after divorce

My friend sister’s husband has filled context divorce against her on the basis of adultery and cruelty. He has some call recordings and filled the divorce case. After knowing that he has genuine evidences, my friend sister agreed for mutual divorce. Now, both have completed the first motion and second motion to be happened. Our point is that her husband has not yet shares/ opens call recording to our relatives because he wants divorce. But if he does the same after divorce then it will be very difficult for my friend sister to live in Society. How can we avoid the said situation of defamation. Can we ask him to write on a plain paper and say he will be responsible for any defamation which will happen in future if he opens call recording to the relatives. Please suggest the best way out, how can we sure he will not do any act which is defamation for us. Thank you