All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the wife passes away, even before the consummation of marriage, then it is incumbent on the husband to transfer the Mahr. Al-Mawsoo‘ah Al-Fiqhiyyah (Fiqh Encyclopedia) reads: “Muslim jurists have unanimously agreed that if one of the spouses passes away before the marriage consummation and the Mahr had been specified at the time of the marriage contract, then the husband is obliged to pay the specified Mahr, whether the wife was a free woman or a slave. This is because the Mahr becomes a binding obligation based on the marriage contract...”
In this case, the Mahr is to be divided among the woman’s eligible heirs. The husband is entitled to a share in her estate as well even if the wife passed away before marriage consummation. Ibn Qudaamah said: “There is no difference between the case of before and after the marriage consummation with regard to the inheritance between the spouses due to the general wording and indication of the verse; and because the Prophet, sallallaahu ‘alayhi wa sallam, ruled that Barwa’ bint Waashiq had a right to a share of her husband’s estate although he passed away before the marriage consummation and had not specified a Mahr for her. In addition, since the marriage is valid and effectuated, then it is a cause for inheritance as with after the marriage consummation.” [Al-Mughni]
If this woman does not have any other eligible heirs – children from a previous marriage, for example - then the husband gets half of her entire estate as a fixed share. Thus, he gets half the specified Mahr and her parents get the other half.
Allaah Knows best.