Ever gracious, he accepted this news and handled the news as a professional. I always enjoyed Leno, since way back in the early 80's when he was a frequent guest on David Letterman (both on his morning show, and then later on the original "Late Night with David Letterman").
I had mixed emotions when he was anointed to replace the legendary Johnny Carson over Dave, since I was an appreciative fan of both.
His humor, though only sometimes self-effacing, was and still is mostly topical. Never hostile or insulting, Jay always took the high road and aimed for the pure comedy. No raunchy puns, racist rants or trashy and vulgar subjects. His was a long and successful run that appealed to a broad audience. He was given a chance to establish his audience, and even though he started slow out of the gate, he eventually steamrolled to the top. And stayed.
Where Letterman never evolved from the frat-boy 'inside joke' shtick that failed to be funny by the time all of the drama transpired, Leno always was broad and entertaining, even after having to re-invent the show early on in his run. His 'Tonight Show Band', led by Kevin Eubanks, was stellar and entertaining. He always seemed genuinely surprised at his good fortune, widespread acceptance and continued success. He connected with the viewer.
Conan O'Brien, on the other hand, seemingly appeared out of nowhere. He was initially a staff writer on HBO's "Not Necessarily the News", then was hired by Lorne Michaels to help revive a struggling "Saturday Night Live". His off-beat approach helped catapult "The Simpsons" to the top, and his contributions to the show were many, from scripts to story and joke contribution and eventually even producer credit.
Like Leno and Letterman, O'Brien's was initially self-effacing humor, and he often used his unusual appearance-- 6'5" height and carrot-orange hair-- as comedy fodder. Again, much like Letterman, his humor was an 'acquired taste'. But unlike Dave, Conan was funny. Consistently. And his band, led by 'E-Street Band' drummer Max Weinberg, was probably the best combo on television. (Until Fallon corralled The Roots)
I would suffer the consequences of sleep deprivation just to stay up long enough to watch the monologues, and was overjoyed when (for a time) the shows were re-aired the following evenings on MSNBC. (I was disappointed when these re-runs ceased.)
Admittedly, I had reservations about the movement of Conan to the earlier 'Tonight Show' time-slot, as his IS a totally different humor than Jay's. (Whereas Leno would cause me to chuckle, O'Brien sometimes made me laugh out loud.) But it was still funny, and apparently someone at NBC thought it was a good idea.
Unfortunately, in this new era of 'instant gratification', Conan didn't automatically unseat Dave from the top of the ratings after vacated by Leno. Six months into the gig, O'Brien is informed that he will be replaced.
No chance to build an audience. No chance to improve ratings or 'viewership'.