I can say that, if a casino is not running a signature ad campaign and also does not gave any form of advertising running on other places, if they have a new product or feature they want to let their players know of, they can simply post about the new product or feature on their announcements threads and their social handles, this can still pass the message if they have a lot of their customers paying attention to their updates.
But nevertheless, every business, not just casinos, deserve to be advertised, they need long term advertisment because is the backbone of the business, with how saturated the gambling industry is today with casinos, any casino not running any form of advertisment is possibly as good as dead - an abandoned project.
Signature campaigns for the long run are good ways to keep the casino in the mind of the gamblers, at least it helps to boost their popularity. But what each casino needs to do is have constant advertising, whether they post it on gambling forums or they post it on their forum announcement, wherever they know that their audience are. They shouldn't stop advertising new features, new games and everything to keep their casino in the mind of gamblers.
Out of sight they say is out of mind while stopping signature campaign might reduce popularity a bit the process of not doing signature campaigns or any form of promotion at all to keep that casino in sight of gamblers will completely take them off the market or their gamblers mind. Unless gamblers love the experience they got from that casino so they keep coming back to that casino even without campaigns or ads but that can't be guaranteed because some people like trying different things, which means you can't completely hold gambler down even with top notch user experience
The point is while stopping signature campaign does not completely reduce a casino's popularity, it's important for a casino to always look for promotional ways to keep their casino in the mind of gamblers.