My prediction is that as people grow up they will start frequenting different parts of the site such as cults, reading powder magazine for a more rounded "lean back" experience, and continuing to browse newschoolers to look at content just not post as much.
Remember, its been 12 years since it started, and we've already processed through one generation of skiers. Some people do leave, some of them do go to other forums, but plenty of them still cruise by to see whats happening or simply look at some solid newschool content.
Hell, I'm 32, and though I no longer slay the forums like I used to, I'm constantly reading news, looking at photos, videos, reviews... etc. Sure I work here, but my habits simply shift. Forums are only like 40% of the site anyways, there's lots of other stuff in here to enjoy.