I disagree. A Trump v. Sanders presidential debate would be a huge media opportunity. Trump would have so many great insults about Sanders, and Sanders would utterly humilate Trump on policy. It would be an epic debate.
Of course if Hillary goes up against Trump, we are going to see one of the greatest upsets in debate history. Trump will utterly destroy her, I honestly wouldn't be surprised if he made her pass out from the stress. There is just so much material for him to work with. His opening line would probably be about Bosnian snipers. He'd still lose the election to her but the humiliation would be total, and her Presidency would be doomed from the start after Trump is done riling up the base.