Personally, I don't see the logic in Chow's move. He is going from one OC job to the other. And, arguably, USC is a bigger stage than a worn down/rebuilding TENN club. If he stayed for another year at USC, he would possibly win another title and possibly have several head coaching opportunites at the NFL level.
By taking the Tenn gig, he is setting himself up for failure. They play in a tough division and have an aging roster. Chances are they won't be in the playoffs next year (although it's FAR too early to speculate on that I guess) so there isn't much of a chance he could end up as a HC in 2006...at least not in the NFL.
As for McNair, Tenn won't let him walk away. If he wants to go to another team, they will trade him, not cut him. He is too valuable to that franchise to simply let him walk away (from a PR standpoint alone). Still, I think he's done.
Even if he doesn't hang em up, he hasn't got much left in the tank. Moving from Drew to Steve (especially with the OLine the Bills have now) would be an upgrade, but a slim one. He has taken too much damage and hates to practice. That won't fly with this coaching staff at all. So I doubt Buffalo would make an offer.
I could see a team like Arizona making an offer, possibly Baltimore. Miami doesn't have anything to offer for him, so they're out. And Cleveland won't break the bank on McNair (just a hunch), Crennel will want to build through the draft and FA.
Just my two cents.