Is the khulʿ contract considered void if the wife does not return the mahr and gold, especially given that consummation has not occurred?

If the khul' (divorce by mutual agreement) was effected with offer and acceptance regarding the stipulated عوض (compensation), then the wife is irrevocably divorced, and the husband does not have the right to take her back except with a new contract, regardless of whether she paid the compensation or not. Ibn Qudamah holds that revocability (رجعة) is not established in khul'.

As for the compensation for khul', it is a debt owed by the wife that she must fulfill. If she refuses, the husband has the right to take her to court.

If the khul' was conditioned upon the payment of the compensation, then there is a scholarly dispute regarding the validity of such a condition. If the khul' is initiated by the wife, it does not accept conditioning upon a stipulation according to the Hanafis and Shafi'is because it is a compensatory transaction (معاوضة). However, if it is initiated by the husband, it accepts conditioning according to the Hanafis, Malikis, and Shafi'is because it is an oath. The Hanbalis did not permit conditioning khul' by analogy with sale.

It is recommended to refer to the shaykh mentioned in the question if he is among trustworthy scholars.