I'm not sure. There's a difference between getting pulled off, and deciding now was the time to leave even though you still have stories you want to tell. When Percy's been interviewed about it, he seems to indicate it was his decision to leave. Like he had done 52 issues, and that seemed to be the right number for him and he wanted to do something darker.
It seems kind of like when Lemire left. It seemed very sudden and people assumed he was removed since he had other ideas he might have explored more, but in really Sorrentino wanted to do other things and Lemire didn't want to do it without him. Sometimes people leave of their own free will, even if there is more stories they have to tell. I think that's the case here.