I don't want to say it's strictly necessary, but not having it will make your life a hell of a lot harder if you want to do anything which isn't with your immediate friend group (where you might be able to get away with whatsapp).
As someone who needs to contact people fairly often and somewhat urgently, it's an absolute pain if I can't contact my target audience on facebook, and I'm one of the few people in my position or similar who contacts people by means other than facebook. It makes my job to recruit people harder, and it means you're more likely to miss out on events that I'm trying to put on for your benefit.
So basically, if you don't have facebook and want to get involved with uni life, you better go to every meetup of the societies you go to, and check your email, texts and whatsapp regularly (as in at least every hour or two during daytime, 8ish-6ish), if you don't then you will have problems keeping up with what's happening.