Freudenthal would have nowhere near as much success in a federal race as he has in gubernatorial races (kind of like Carcieri running for Congress in RI), but you're right that he may beat Cubin even in a presidential election year. I don't expect for Cubin to run again, though, and Freudenthal is unlikely to run for anything else until he finishes his second term; if Freudenthal does run a "freebie race" in 2008, it may be against Senator Enzi, since the reward is much higher.
I also heard the word "retire" escape the lips of a Wyo Republican concerning Cubin. Hope that's true!