In a less demagogic manner, the game mechanics define the truth of the game world, and the game mechanics clearly say that this is a new character (because he has a "began his career" family history entry) as well as that the old one is dead.
So, I would treat this in-game as exactly what it is: Someone from the same family with the same first name who claims to be the resurrected dead guy. Obviously, he's a bit nuts or something.
