NBC took a risk. It didn't pay off this time. As I mentioned earlier, the reason why this situation came about is that NBC had an embarrassment of riches of talent, with Leno and O'Brien. If they only had one great star, then none of this would have occurred.NBC (and Jay) screwed up big time. Oh well.
As it is, NBC still has a problem. Their television line-up is still too expensive, vis a vis that money they're going to be making from advertising. So either they need to come up with some other low-cost programming to present, for at least a few more hours per week than will be the case after Leno is gone from the 10PM slot, or they're going to have to play hard-ball with the cable companies and satellite services, regarding retransmission fees, so they get more money that way. However, the latter approach is problematic. Even though Fox just played that game and gained a bit, NBC may not be able to, due to commitments they're probably going to have to make to get the Comcast acquisition approved.
I think it may be time for NBC to seriously consider structuring prime time the same way Fox does, 8PM-10PM Eastern Time (instead of 8PM-11PM).