Generally, the rule is that the "petition dies with the petitioner." The main question is what was the relationship between you and the petitioner? Was the Petitioner your spouse? Upon the death of the United States citizen petitioner spouse, the approved I-130 petition is automatically revoked pursuant 8 Code of Federal Regulations section 205.1(a)(3)(i)(C) and the beneficiary must affirmatively request reinstatement of that revoked petition pursuant to 8 CFR section 205.1(a)(3)(i)(C)(2).
USCIS will consider the facts and humanitarian considerations of your particular case. If reinstated, then the beneficiary is able to file for adjustment of status to lawful permanent resident or consular process. If reinstated, then you will need to obtain a substitute sponsor who will need to file a Form I-864, Affidavit of Support.
You do not need to send the I-864 before the I-130 approval is reinstated. The substitute sponsor will check box (f) on the I-864, indicating that the original petitioner is deceased and that they are the substitute sponsor. The substitute sponsor will need to provide proof of U.S. citizenship or lawful permanent residence and financial documentation proving s/he meets the appropriate income requirements for his or her household size. If the petitioner was your parent, child, or sibling, then there is probably nothing that can be done and you will need to find a new petitioner because the reinstatement provision only applies to a spouse of United States citizen who was a beneficiary of an approved I-130 petition.
From the facts presented, it does not make sense that you would send a Form I-864, Affidavit of Support, when the underlying petition has been revoked and the petition was not reinstated. Plus, a Form I-864 is only required when the beneficiary is eligible for adjustment of status because it is filed with the I-485 adjustment of status application. If you have further questions about reinstatement of an approved I-130, it would be wise for you to consult with immigration attorney with extensive experience in I-130 reinstatement and family immigration.
Michael Shane and Evan Shane, Immigration Attorneys
Miami and Fort Lauderdale, Florida
Shane Law
-- Michael Shane