Fumito Ueda will remain at Sony as a contractor until his work on the upcoming The Last Guardian is completed, but Sony has officially confirmed to Gamasutra that Ueda has left the company's employ.
Sony was quick to claim, however, that these circumstances will have no affect on The Last Guardian's development and claimed that Ueda was fully committed to completing the project.
We're inclined to believe Sony on this occasion. In interviews Ueda has always appeared fully committed to his titles, considering the huge investment he puts into each game he develops. Many of his projects have been delayed in order to tweak tiny details and get everything in the game working as he originally envisioned.
In short: we're not worried. It's impossible to say with any certainty, but this most likely won't affect the development or quality of The Last Guardian. We hope.
Confirmed: Ico Creator Fumito Ueda Leaves Sony [Gamasutra]