I wouldn't say face book is dying off exactly...more like separating off into various specialized cliques. One of the groups I admin, the TOPS Knives Users, has grown from 600 members to 2,949 members since last July, still gains about a dozen members a day, and has a LOT of daily traffic in chat and photos. Mostly a good group of people. The Spartan Knives Users Group I started last June has grown from a handful of members to almost 600 in the same time, but I am very selective in how I approach that group membership due to the niche-y nature of their knives and their target market. I encourage active duty and veterans, as well as first responders, and discourage mall ninjas.
My Fiddlebacks always get good responses on some of the knife groups I am in, both from users and collectors. The thing I do like about facebook is the ability to instantly post and share photos without a need for a hosting site, somewhat like instigram but larger and not geometrically limited.
That said BF has worked out well for Andy, and I don't see him wanting to leave anytime soon, and we have a great community here in this forum in my opinion. While I like to share pics of Fiddlebacks in a lot of places on face book, and regularly get into discussions on the knives there in different groups, I think it would only work well if at some point, for whatever reason, Andy made the decision to leave BF and we all gathered there and reformed the community. I do know several folks from here are on FB and in my friends there. Derrick started the group "Amazing Knife Photos" and so I post a lot of pics of Fiddlebacks there and get a lot of good responses.
One thing I have noticed is the self segregation of collectors and users on FB, much like on the majority of BF. It would be a rare thing to create the adult-like and more mature mix of both on FB the way we have here in this forum.