Loss of social network is a big concern among pre-retirees. When you will retire from your career, you more than likely won’t be seeing your colleagues and / or work friends everyday but that doesn’t mean that they are gone from your life forever. If you had good work and personal relationships with your co-workers, then these friendships may be strong enough to continue once you have left work.
Like all relationships, however, you need to make time and work on your friendships to stay connected.