His tweets and then he retweeted the following article from Nerdist.
garywhitta: My year of work in a galaxy far, far away is done! I’m onto my next project, adapting @mrmarkmillar’s STARLIGHT for 20th Century Fox!
garywhitta: This is by far the most I’ve ever enjoyed writing a title page. See you in 2016! #MTFBWY
Gary Whitta Departs STAR WARS Standalone Movie for STARLIGHT « Nerdist
"While The Hollywood Reporter article makes it sound a bit like something unseemly happened, the news of a writer departing a project after completing a draft is by no means surprising. (Case in point: look at what happened with The Force Awakens after Michael Arndt left and J.J. Abrams and Lawrence Kasdan came in for the next draft.) Rather, it sounds like the increasingly busy Mr. Whitta simply completed his contractual obligation and is moving on to the next item on his dance card."
In a statement, Gareth Edwards said, “Gary has been a wonderful, inspired contributor and I enjoyed working with him tremendously. I’m so grateful for all of his contributions.”
Whitta also said, “The year I spent working with Lucasfilm on this Star Wars film has been by far the most rewarding period of my entire career. As a lifelong Star Wars fan I’m deeply grateful to have had the rare opportunity to contribute to a new chapter in its ongoing cinematic legacy. The film is going to be amazing.”
nice catch. Would love to say that was planned. 
