Is khul' permissible for a woman, and do the husband's rights over her cease immediately upon khul'?

Khul' is permissible if there is a reason for it. There are indeed Hadith that warn against it if the woman seeks it without a reason. If khul' occurs, the woman gains control of herself, and her financial rights over the husband, and his over her, are waived. The husband has no right to take her back except through a new marriage, in accordance with the Almighty's saying: "But if you fear that they will not uphold the limits of Allah, then there is no blame upon either of them concerning that by which she ransoms herself."