I cannot honestly believe for one moment that jk Rowling doesn't have complete control over this situation. If she is not involved it's because she chose not to be, for whatever reason, but no one has the power or balls to exclude her from her own creation, she would have made sure of that.
At the very most, some of those actors could have refused to take part if she did, that's as much sway as they have.
Really honestly and with all my heart, I believe we are getting closer to the time when everyone is going to have to apologise and admit she was right. She's just holding on until the optimum moment. If she hadn't become a billionaire through her talent, she would have cleared up at poker.
(of course, I could be wrong. Can you imagine the phone call or meeting where they told her she would not be involved and her just saying OK, tho)