If your friend officially revoked his sponsorship by notifying the U.S. Immigration Service (USCIS), he will no longer be held responsible for the green card petition that was submitted. His wife may have a claim to the home depending on how long they were married and the laws of the state where the marriage happened. Your friend should consult with a divorce lawyer since it is a contested divorce.
The other responsibilities: 1) the husband has incurred a legal and binding obligation to the government due to his having signed the I-864 Affidavit of support contract with the government. He guaranteed the government that she would not become a public charge or take welfare benefits, and if so, he has to reimburse the government or the state, dollar for dollar.
2) Also, the I-864 can be used by the wife as a third party beneficiary entitling her to get support from him in excess of that required under the state divorce law. This man needs a divorce lawyer and an immigration lawyer.
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