As of this point, I think Roman may possibly retain. If anyone has noticed, Cody has had more interactions with the Usos', Solo and Heyman than Roman. They haven't even brawled yet as compared to Roman's other feuds. Also with the rumored return of you know who, who is to say he won't screw Cody over and Roman retains to get that championship record. There's history there. Now if Roman does retain, who dethrones him?
Big E at next year's Mania if he returns? But have him solo and not a part of New Day.
Bron Breakker?
Seth Rollins?
Jey Uso?
Solo on some Batista/HHH WM 21 storyline?
Who knows?
Personally Brock should have beat him at Mania 38, and we could have somehow gotten Seth vs Cody @ Mania for the belt. But then we wouldn't have gotten the Bloodline/Sami storyline.