I thing something weird will happend and Barret will win the title, then Orton will blame it on Cena who might appear to be victim of the circumstances.
The Miz won´t cash in before the Royal Rumble, why would he cash on Barrett? it won't generate heat for the Miz, it will take heat from Barrett and will make him and Nexus a joke. Besides, he has plenty of months aftert Mania to cash in and would make more sense if he does at Mania.
This will set up Barrett VS Cena at TLC and Orton will cost him the title, then they will cost each other to win at the Rumble and the Elimination Chamber and they will have a final showdown at Wrestlemania but not for the title, which is unlikely.
This will set up Barrett VS Cena at TLC and Orton will cost Cena the title, Orton will win the Rumble and Cena will win the title from Barrett at the EC after the Undertaker (if he is healty enough) distracts Barrett and this set Orton VS Cena (Title) and Barret VS Taker (for what happened at Bragging Rights).
In each scenario there is the big possibility of Cena going Heel after he realizes he can't stop Orton's momentum but not before Wrestlemania.