Many of those top quality posters who joined mixer campaign aren't gamblers, so the drawback they might not post in gambling board.
I'm not sure if we will see a new casinos campaign very soon after the mixer ban begin, but the current casinos can volunteer hiring them, just like some top users are wearing Duelbits signature.
But, how did you know that they are not gamblers? It's possible that a user isn't picky, and there is an opening in the mixer campaign, so they joined it. Or the pay rate for it, and other conditions are much better, so they switch on it. If you are on a gambling campaign, like it or not, you will be making some gambling posts. It was only a few posts anyway, and most of the posts are still going to be spread in many areas of the forum.
Mixers and casinos are different services. So even if there is a new casino that will spawn, right after the banning date, I am sure it has no relation to the mixer. And even if let say a mixing service will create a casino with a mixing feature, they won't still be allowed here.