It is necessary in that it is the metatext behind everything in Don’s world revolving around dishonesty. He’s not just an average philandering ad man who is good at the art of bullshit. He IS bullshit. Furthermore, as we saw in the first episode of this season, Don has very clear ideas of the creation of Dick. They may or may not be accurate. We don’t know and neither does he. We see that, thanks in part to a traveling hobo, Dick/Don believes his adoptive father to be a dishonest man. Don feeds on dishonesty as much as he is tortured by it; I am not convinced that this is the death of Dick.