He is going to be so over by the time December rolls around. People will be respecting his heel work if he can really get in a groove, as well as in their feelings. I also don't think he's gonna retire the Universal title, and we will get someone "saving the legacy" on his last match. (Probably Cody). Can also set up a post-match promo or Raw After surprise promo where the new champion convinces Cena to look around the fans do respect him. He needs that wholesome sendoff, and cements him for future one-offs as a beloved legend.
Randy as first challenger, although might be for the millionth time, is someone with as much respect, that the fans totally won't turn on, and Cena should be able to actually remain heel.