It wasn't hard at all. I keep in touch with the people that matter to me using email, phone calls, text, IM and Whatsapp (and then they went and got themselves acquired...)
It's arguable my social life might have been even better had I never left (missed invitations, lacking fodder for small talk with mutual acquaintances etc) but I clawed time back in my day for other things. I also don't have to worry about things like FOMO, social media generated envy, pointless social oneupmanship and the like. YMMV
I am however missing out. You'd be surprised how many companies and such that jump at the opportunity to become locked in. Many simply stop entertaining other communication channels.
since I am no longer easily invited to events, all but my close friends bothers inviting me to things.