I promise you not a single response in this thread on this website will be "no I couldn't live without Facebook." Everyone here knows that one user would be made fun of and thought of as a loser and "fag."
In reality I'll tell you why it would suck if I lost it. I would lose a great networking to a great group of friends I have around the world, who I don't often get to talk to on the phone, and I don't like emailing, so Facebook is convenient in that sense. I also have a place to see how old high school friends who I still stay in touch with are doing. It's a pretty useful and well done networking site. Could I live without it? Yes. But then I'd need to find other ways to accomplish staying in touch with my international friends.