Funny thing is that last night's ending could have planted the seeds for a Cena heel turn:
When Seth Rollins threatened to curb stomp and paralyze Edge that should have had Cena like "

..... you know what.... sorry Edge but I just refuse t bring those b*stards back

" and he turns his back and walks away while Seth curb stomps Edge and they end the show with parametics tending to Edge. The next week have Christian come out and call Cena a worthless b*stard for not saving Edge and have Cena be coldhearded like "

I don't give in to threats" but have the entire locker room not look at him because they also blame him for Edge which eventually have Cena be like "

This is what you turn me into Seth... now let me embrace the hate" as he captures Rollins and gives him an Attitude Adjustment off the stage to make Michael Cole go "

CENA HAS GONE TOO FAR DAMNIT! HE'S BECOMING A MONSTER!" and show the little kids in the crowd

at what their hero has become.
Cena realizes he has crossed the one line he vowed to never cross looks at himself and goes "

All of this and for what... for The Authority to come back? Fine... I grant the Authority to be let back on television" in which the next week they come back and congratulate Cena for his decision only for Cena to grab Stephanie and give her the Attitude Adjustment letting HHH know that a price had to be paid for allowing them to be back on tv and he'll be next if he wanna go at it. HHH looks at Cena like

and figures its not worth the trouble since he's back on tv.
That's when that vigilante Sting comes out and tells Cena he's too far gone but he still sees a glimmer of light still shinning in him and that he can be saved, Cena too numb from the previous weeks looks at Sting like "

I'm already dead, there's nothing you can do" but HHH comes out and for retaliation of what Cena did to Steph and because of his hated of Sting he'll book his two enemies to face each other at WrestleMania and Sting accepts because it'll be his chance to save Cena's soul.