I HOPE... at various points in the match Barret and Cena square up and have words, gradually building the tension. Then towards the end, with the tension seemingly at breaking point, Cena grabs a chair giving the impression of him saying "f**k it, I don't care about the consequences". He goes for Barrett who ducks and he takes out Orton who is right behind him.
Initially, it looks like Cena is devastated with what he did but then a slow sly grin comes across his face before he embraces Barrett. Anything after that would be good, but best scenario would be Cena to do a quick 3 count but with Orton's foot just under the ropes, really really subtle so hopefully not too many people notice. Have Nexus celebrate in the ring but then the next night on Raw it's revealed that Orton is still champion. With Cena then a fully committed member of Nexus, things would get very interesting.
I THINK... Cena will reluctantly let Barrett win, then hit him with an attitude adjustment setting up a feud between them which will lead to Cena becoming champion again. It will be shite.