Many subs are still private or restricted, but they might not have the critical mass to actually make a difference. Most likely, the IPO will go as planned.

My guess is, that once the mod tools stop working, quality of every sub will decline over time. As a result, users will gradually start looking for a better place with fewer spam bots, reposts and unhinged individuals. If that happens, the ad revenue will also decline during the next year or two until Reddit will be about as relevant as Tumblr.