My Jiu Jitsu gym heavily uses Facebook but they're smart enough to recognize that not everyone (even the people that have an account) checks it regularly so they notify the members through other means. Lately they've been telling people to be on the lookout for a text message they're planning on sending so, it sounds like they're recognizing that Facebook use is waning in a meaningful way.
I haven't had a Facebook account in 12 years and haven't missed it one bit. I don't expect everyone else to do any extra work to accommodate my preferences. I didn't ask my gym to text me. The just started doing it.
Time and again for the last 12 years I've found that if there was something someone needed me to know, they found a way to contact me and, if I needed to get in touch with them I found a way. Just like we did for many, many years before Facebook started.