NBC is making another huge mistake.
First, Jay Leno will never "go away." He will agitate behind the scenes, always, to improve his standing. He will never stop trying to maintain control of the Tonight Show.
Second, Jimmy Fallon should stay where he's at for another decade and continue to make a show that is better than the Tonight Show will ever be. Once he moves to the earlier time slot, the dynamics of what is expected of him will change and he won't be free to do what he's been doing. He will have to answer to affiliates and advertisers and that will water down what he is good at, which is damned near everything Leno can't do.
Third, the guy who should be handed the Tonight Show is Jimmy Kimmel.
I wouldn't sign a single deal with anyone if I were Jimmy Fallon; NBC destroyed Conan O'Brien (when was the last time you cared about Conan?) and they let Leno do it. The fact that the gave Leno BACK a job he couldn't hold indicates that Leno is simply looking for the next human being to destroy.
Leno cannot destroy Kimmel because Kimmel is the anti-Jay Leno. It's in his DNA to be the heir to Johnny Carson, should that remain possible in the changing landscape of television.