What is to be done with the remainder of his money, which is mixed with lawful and unlawful sources, and most of it is gone, knowing that he has repented and needs capital for a permissible business?

The loss of blessing from haram money is a natural consequence. The owner of such money must repent sincerely and calculate the amount acquired from illicit means. If there is a specific owner, the money must be returned to them or their heirs. If it is impossible to reach them or their heirs, the money should be given in charity for the benefit of Muslims or distributed to the poor and needy. If the owner himself is in need, it is permissible for him to give it as charity to himself and his family. If this friend repents as described, his wealth will be purified, and the return of blessing to it is hoped. He is not required to acquire new capital to start a permissible business.