In my opinion , Facebook is essential for online industry professionals, I hate to think of anything being required that strictly. I'd say that if you have an online presence, are accessible, and have a way of demonstrating the online skills which you are marketing/using in business, there are no social networks you MUST be on.
But that does not answer the question. And since quitting anything is a personal experience, I can only share my own. Before I entered social media marketing, I was only a casual Facebook user, and I did quit my personal account--it was just too connected. And it felt refreshing not to be obligated to check status updates and post my own. But as a digital marketer, I feel incredibly withdrawn and disconnected if I cannot access my social networks. Recent studies have suggested we are more addicted to social media than other vices like caffeine and chocolate. As semi-depressing as that is, I think it would feel like any other withdrawal to up and quit Facebook at this point in my career: hard at first, but easier with time.