Handles is the greatest companion in the history of all of Doctor Who. He will never be topped ever. Anyone who believes Handles is not the greatest companion of all time must be destroyed on sight. He was so great that if he appeared for more than one episode the fandom could not have handled (Get it? Handled. It's a pun.) his greatness. So Moffat was forced to kill of the greatest companion of all time. However in reality the show would have been reborn as Handles Who. If you dare question his greatness you are an enemy of the state.
His death scene is the saddest moment in Doctor Who. No wait, his death scene is the saddest moment to ever exist.
Handles is always canon. No matter what there is, he is canon. He is the constant. The true reason there is canon.