Is it permissible to stipulate that the deferred dowry (mu’akkar as-sadaq) is not a debt upon the husband except in the event of divorce, such that the wife does not become entitled to it upon his death? And what is the accepted wording for this? And what is the opinion of the Maliki and Shafi’i schools of thought on this issue?

The deferred dowry is a debt owed by the husband, and he must pay it unless the wife waives it. She has the right to voluntarily gift it to him. If the wife waives the deferred dowry on condition that she not be divorced, and then the husband divorces her a short time later, she has the right to reclaim it. However, if he divorces her after a long period, or if the divorce was due to an oath and not intentional, scholars differ regarding her right to reclaim it. The Malikis believe that she cannot reclaim it if he divorces her after a long time, whereas the Shafi'is believe that she has the absolute right to it unless she waived it gratuitously, and they consider the condition of not being divorced invalid.