I don't think everyone leaves en masse but I do expect a pretty big impact already, and considering they're attempting to IPO I doubt any of this is a good look.
Digg and Tumblr?
Force communities back open, how? I've read countless comments over the past few days about how Reddit can just reopen all the privated subreddits with new moderators, without explaining where those new moderators were going to come from.
Curating and maintaining a community takes a LOT of effort, and I'm not convinced it's that easy to find people willing to do it for free. Just think about open source projects and how many have died when the sole maintainer called it quits.