Logically, HeroesWorld would need to adapt to the changing reality and think about how to integrate its rating with lobby ratings, otherwise the HeroesWorld rating will simply freeze—it's only a matter of time. But remembering how opaque, mysterious, and strange the last update of the HeroesWorld rating was—silently throwing a wrench in the works on the fly for Igromant, who was saving and improving it—most likely this adaptation won't happen.
The HeroesWorld forum will only die if another forum appears to replace it.
A forum—as a platform for communication—is generally a good, universal tool. And Discord won't fully replace it.
Activity has already decreased, but for it to completely die off—I think that's unlikely.