This is rather disheartening news, and something I was not aware of. Like others have mentioned here, Wally Pfister is synonymous with Nolan. Actually, when cast in that light it is perhaps not so saddening, at least from Pfister's point of view. It should benefit him greatly to work with other directors, maybe letting him express his talents in ways he may not have previously known he desired. Still, much of what I love about Nolan's films is a product of Pfister's camera work. Here's hoping he is free to work on Nolan's next film (a Howard Hughes biopic, if I remember aright).
I am definitely in agreement with jibran on the subject of a potential future collaborator. Emmanuel Lubezki would be a brilliant addition to the Nolan crew. I absolutely adored Lubezki's work on Malick's The Tree of Life, and I would be overjoyed to see these two at work on a film.