I'd probably keel over. As a long-time forum user, I wouldn't know what to do with myself without the added conversational stimulation you can get online. I'd probably start calling my friends at 3am to say "Hey, have you ever thought about how that duster in Beauty and the Beast was a whore, but they just act like it's funny? Why is sexuality funny?"
And soon I'd have no friends.
I "grew up" with the internet. I don't watch TV, I haven't seen tons of movies, I don't know much about pop culture outside of the people who truly interest me. I know everything I want to know about any topic at any time.... I can speak on many topics and expect others to be able to do likewise.
And now that I live abroad, things like Skype and Messenger systems keep me in contact with western culture. It would be a hard blow.