What I've noticed is that I actually meet people IRL more often now, because the events I get information about are the ones that really matter to me, and they don't get lost in a constant buzz of less important but attention-grabbing stuff.
I also realize I can miss talking to someone. It's a feeling I haven't had in a long time, because people used to show up in my feed every day and it was like they were there anyway. Now I can get a sudden urge to just shoot a few texts back and forth with someone about something that's actually meaningful and not just the usual facebook wall banter.
I'm quite introverted, so being selective is something that suits me well, but facebook also made me even more socially lazy and avoidant than I really am.
Maybe I just have friends who don't care too much, but I wouldn't expect any of my friends to notify me if they're going to a run of the mill event without me, but they would suggest it/notify on Facebook about it. It's a lot less personal, I feel, to notify someone on Facebook than to message someone personally and invite them. Chances are, they'd see I'm no longer on Facebook and think I've gone into some kind of social seclusion.
It also doesn't help solve the problem of me finding something I want to go to (that my friends might be interested in) but they didn't see themselves. There was recently a Studio Ghibli film showing in my city, and after I found it on FB, I suggested it to two friends and we went. I wouldn't have found that event without FB, and even if I did, it would feel awkward (for an equally introverted person like me) to specifically message the two people and ask - now they have some kind of obligation, and they can't claim they just haven't checked Facebook in a while if I sent them a text/Telegram/whatever.
However it has forced me to be more engaged with my friends, since without Facebook they have to make a concious effort to invite me, rather than spot my name on a list. I've spent more time personally messaging and catching up with friends as a result.
Facebook makes keeping up with people frictionless, but relationships thrive on doing it the hard way, and giving up time for each other. Facebook makes it easy to have a thousand acquaintances regardless of how many deeper friendships you have.
I've never really been interested in going to a random party or event I wasn't directly invited to. I mostly got spam when I was using Facebook.
Do you go to parties? Serious question. It's hard to discover events without Facebook these days. It's the only place some promoters advertise.