Facebook will no doubt take a few hits once steemit starts to catch on, but don't assume they won't be able to come up with ways to keep their massive user base, perhaps finding ways to reward users for receiving a lot of likes. They might even attack steemit which wouldn't be all that hard with all the money they have and some vulnerabilities with the whole concept of steemit. Hopefully the awesome community we have now will find ways to protect against anything like that though.

The only way I see Facebook going down is if the laws change and they start actually feeling pressure for all of the "questionable" things that they stand for. But Facebook doesn't need to go down for millions of people to do great things here.

Reddit probably won't survive steemit though....