If anything, Conan might find a way to take over for Letterman someday.
I was under the impression Craig Ferguson taking over the Late Show once Letterman retires was unofficially a done deal. I love Ferguson but I'm afraid that might not end well given CBS's demographic. Same goes for Conan potentially taking over for Letterman.
Ferguson has been very up-front and public about not wanting anything to do with The Late Show, and honestly I'm thankful for that; moving to 11:35 would destroy his program, which is much more akin to Pee-wee's Playhouse than a traditional late-night talk show. A while back, there was some talk of CBS desperately hoping that Jon Stewart would be interested, but he seems content at Comedy Central.
Conan just re-upped with TBS through 2015, so he isn't going anywhere anytime soon.
If anything, my money is on CBS throwing everyone a curveball and giving The Late Show to Ellen DeGeneres.