You need to have a substitute sponsor in such an event. Please read the page 3 of I-864 it explains what to do under such circumstances.
What Is a Substitute Sponsor?
A substitute sponsor is a sponsor who is completing a Form I-864 on behalf of an intending immigrant
whose original I-130 petitioner has died after the Form I-130 was approved, but before the intending immigrant obtained permanent residence .The substitute sponsor must be related to the intending immigrant in one of the following ways: spouse, parent,mother-in-law, father-in-law, sibling, child (at least 18 years of age), son, daughter, son-in-law, daughter-in-law, brother-in-law, sister-in-law, grandparent, grandchild or legal guardian.The substitute sponsor must also be a U.S. citizen or lawful permanent resident.
If you are a substitute sponsor, you must indicate that that you are related to the intending immigrant in one of the ways listed above and include evidence proving that relationship.The beneficiary must also file this form along with a written statement explaining the reasons why the Form I-130 visa petition should be reinstated, having been revoked following the petitioner's death. The beneficiary must also include a copy of the Form I-130 approval notice.
If Democrats Had Any Brains, They'd Be Republicans
Democrats - Brave enough to KILL our unborn, just NOT our ENEMIES!