At this point, I think that the most likely scenario is going to be Orton winning the title at Unforgiven. I feel it will play out with Cena's agression getting the best of him, and causing a mistake of some sorts. Orton picks up the title. He retains in a rematch at Cyber Sunday in some type of gimmick match (Steel Cage? Falls Count Anywhere?). From there, I can see two things happen. The first would be to insert Triple H into this feud and have a triple threat match at No Mercy. I'm not so sure this will happen as I think Triple H may be involved in a match with Umaga at No Mercy. However, I would think another match between Cena and Orton would be a bit excessive. For the time being, I'll say that we will see Orton and Cena go at it again at No Mercy, maybe with the fathers in the corners or something. Orton retains by cheating or even getting himself disqualified.
This leads us to Survivor Series, where I think we will see a team of Orton, Kennedy, Carlito, and Umaga take on Cena, Hardy, Triple H, and Cody Rhodes in a Survivor Series Elimination Match. Lets have the faces go over and then at Armageddon, we see HHH-Orton-Cena, and Orton takes the fall as HHH wins the title. From here, Orton is gearing up for a Mania program with HBK and the build towards HHH-Cena 2 for WM 24 is on. So back to the original question, Orton will be champ and a reign from Unforgiven until Armageddon (3 Months) isn't too bad at all.