Not true, Nolan is still going to be busy for MOS, recently he gave an interview where he mentioned about his part in MOS movie. His last four movies have earned WB 3.5 billion (BB, Inception, TDK, TDKR) that is a Lot of money, WB would have to be crazy to let him go. Of course he would Not be directing any more comic book movies. Lastly, Nolan is acting as an Executive Producer for Wally Pfister's movie - Transcendence (Wally was a DOP for many Nolan movies) who will be directing his first movie (that is rumored to star Tobey McGuire, Jonny Depp and Christian Bale) and the studio is - WB. Now, if Nolan were to leave WB that would not have happened.