> If only a minority is out, they will just be outcast.

My kids do not have a social media presence, we have parental controls set on their devices, and the router only lets them online for a small window of the day. They still manage to communicate with friends via email, shared Google docs, phone calls, and actually meeting up. (Remember when people would agree to meet at a particular time and place, and then just show up with no further discussion? It still works.)

I think they'll be fine.