It's hard to tell. Some may return in the future, but I'm not allowed to say much regarding why that is at the moment. I do believe that if the massive amount of users came back all at once, it'd be easier to get them to stay since a lot of them left because their friends were leaving, you know? If this happened hope the forums would become active and different enough to satisfy most of those that left. Seeing how many of the prominent forum users from then enjoy the the main site a lot more since groups and comments on posts were introduced there, it makes me wonder why they can't do that on the forums as well? Or at least make more use of it. I do have other theories of the fate of the forums, but, again, I can't say much regarding that as of now.