Is the husband entitled to take the mahr in exchange for divorce, despite his ill-treatment of his wife, abandoning her, and refusing to spend on her?

If a husband abandons his wife and refuses to spend on her without a valid reason, then he is an oppressor. The wife has the right to take the matter to a judge to compel him to live with her in kindness or to grant a divorce. The husband does not have the right to put pressure on his wife to free herself from him (through khul'), and if he does so, the khul' is invalid and the compensation must be returned.