I do not think Reddit is going to have a mass exodus in the same way that Digg did back then, no. Times have changed far too much for that to be the case.

However, "karma" has no deadline, and I do think that overtime we'll see Reddit decline and the root of the cause will probably come back to this, in some shape or form. I've even heard people in my "normal" circles say that after being met with the "This community is private" this last week, they already don't like their reliance on Reddit.

Twitter and Facebook are a bit different in this perspective. Facebook tends to have close ties to friends/family, Twitter does kinda but not to the same extent - but quite a few people do use Twitter because of celebrities and "bigger people" being on there.