Before his death, the man wrote a power of attorney on the car with the right to sell, or...

Yes, it is cancelled.

In accordance with Clause 6, Part 1, Art. 248 of the Civil Code of Ukraine, representation by power of attorney is terminated in the event of the death of the person who issued the power of attorney, declaration of his death, recognition of his incapacity or unknown absence, limitation of his civil legal capacity.