Is the car still considered the property of the questioner after the dispute that occurred between him and his grandfather, and the grandfather's statement that it was his sustenance, or is that considered a revocation of the gift, especially since the grandfather suffered from dementia after the incident and passed away, and the car is registered in the questioner's name?

The car is not considered a valid gift to the questioner from his grandfather unless the grandfather explicitly declared it as such and had witnesses to it. Otherwise, the consent of all heirs is necessary, because the grandfather's action could be interpreted as either a gift or a loan, and a loaned item must be returned to the estate. A man's statement, "This is my son's generosity," or "This is my son's beast," does not confer ownership upon the son unless it is witnessed as a gift. The complexity further increases because if the grandfather made a gift, he has the right to revoke his gift according to the Shafi'i school of thought. Resolving this dispute requires a judge's ruling, and this becomes even more crucial if the grandfather's mental faculties were impaired at the end of his life, due to the impact this has on the validity of contracts.