Doubtful that would ever happen Francois. The NBC affiliates wouldn't replace the show; they'd risk getting disaffiliated.
As an aside, I went back and found the original MSNBC article written about the proposed changeover when it was announced in 2004. It highlights the fact that, even in 2004, Conan O'Brien was only drawing about half the viewers that Jay Leno was (2.5 million vs. 5.8 million). Fast forward to 2009, Conan O'Brien is drawing about 2.5 million viewers @ 11:35, while Jay Leno is drawing about 5 million viewers @ 10:00.
So, to me, it's not surprising that Conan O'Brien isn't beating David Letterman, nor is he living up to precedent set by Jay Leno, in terms of number of viewers. They've all maintained the same size audience in 2009/10 as they had in 2004 -- i.e. those watching late night shows, on the whole, like a particular host and tend to stick with them.
Basically, my point is that the whole changeover was a complete waste of time as it hasn't done anything to bolster NBC's position -- if anything, it's only made it worse by reducing their ratings in the 10 pm and 11:35 pm timeslots. Regardless of their timeslot, it was and still is highly unlikely that either one would ever see their ratings improve significantly, especially given that there was no marked increase over the previous 5 years. Thus, from a business perspective, NBC's decision to try to return things to the way they were makes perfect sense -- though, it sucks that it comes at the expense of Jay Leno and Conan O'Brien.