If you look at arfcom or other national forums, they are still very active other than the hometown boards. When I'm looking to research something or get entertainment, there is more of it at a big national site than a small one.
MSGO used to be a busy forum, but many have left it to chat on Facebook pages. For many, Facebook is easier to use and quicker than a traditional internet message board and I find that there is more local real-time info on the FB pages.
It is a trend that extends beyond chat and into commerce. 5-10 years ago, a business MUST have a web page to be considered somewhat legitimate. Web pages are a pain to keep updated and then you get constantly criticized for the page looking cheap or outdated or lacking functions that are readily available on Facebook, and there are always costs and upgrades that have to be managed. Expectations are that every website must function like Amazon or every chat board functions like arfcom or others. That isn't financially feasible for most businesses. A Facebook page is free, intuitive, and includes a ton of features right out of the gate.
Gen X and older consumers (that's me) often have a different set of expectations than Gen Y and Millennials. We are used to waiting for something and then we took it for what it was, knowing that eventually there would be updates, changes, or new information. The new phone book was a big deal, or you had to go to the grocery store to see a car magazine to get a glimpse of the new Mustang, or you had to go to the library (or find a knowledgeable person) to get your question answered, or you had to wait until Tuesday night to see the A-Team on a local broadcast channel. Not much different than when news came via the train or mailman 100+ years ago.
The younger generation wants it all now and they want to see change immediately. That isn't wrong, hell we made them that way because we wanted it too so we invented it.
No, I don't think FB killed the gunboards but it did stomp out a lot of the smaller local ones.