First I'd like to know what the hell is Principal Game Designer. Sound like just step up from Senior. When Ion started replacing Chilton he straight up got Assistant Game Director title.
Only way they would can Ion is when WoW got huge drop in sales or subs (generally profits), not because some forum dwellers don't like him. Probably eventually he just resign and switch project or job when he will be burnout, but Ion seems to be more passionate about WoW than previous lead devs. He started as player after all.