I believe that Jay Leno should have left The Tonight Show. It was clear that he was really not needed for the show anymore and that NBC could have gotten better rating with a new host like Jimmy Fallon. I just don't think though that the show will continue to get good ratings.
Jay Leno is a funny guy, I often watched his show and enjoyed it a great deal. There comes a time for everyone when they must pack it up. Jay wasn't ever bad at what he did, but, the network had the right to pursue a younger host in the hopes of achieving a younger, and more lucrative viewership.
No, Jay Leno should not have left the Tonight Show, because he brought in big ratings. Jimmy Fallon's ratings are already suffering by comparison. They are at Conan's levels. Jay Leno thought the people that he worked with were his family. He should have been allowed to leave on his own terms.
He shouldn't have left the first time. I know what he did to Conan Obrien was messed up,but now he has Jimmy Falon on there, he was wrong in both ways, Conan is just a better person for the job, He should not have done it the way he did. I doubt he cares though.