What happens to the mehr amount if divorce happens before the marriage is consummated?

If a specific mehr amount was agreed at the time of nikah and the couple divorces before the marriage is consummated, the husband owes the wife half of the agreed mehr, per Quran 2:237 — she keeps this half regardless of who initiated the separation, unless she or the person holding her marriage tie voluntarily chooses to waive it. This is a direct, explicit Quranic ruling, not a matter of scholarly disagreement.

If no specific mehr amount had been agreed upon at the time of the nikah, Quran 2:236 instructs that the husband should still give the wife a reasonable gift (mut'ah) appropriate to his means, even though no formal mehr obligation had crystallized — the underlying principle in both cases is that a woman should not walk away from an unconsummated marriage with nothing, given that the marriage contract itself created real obligations toward her.

Source: Quran 2:236-237.