Wrongfully declared dead?

I have a relative who was declared dead in error. It's a long story, but he was in an accident and suffered some memory loss. We discovered that he is a alive and he found his way back to us. The problem is that a death certificate was issued and his property and assets were distributed by the probate court. He is insisting that all his property be returned to him as he wants to resume his life. How can we go about reversing the probate order and recollecting his property? Some of the family is not cooperating. Also, what can we do about the death certificate? Is there a way it can be discharged or canceled?