I think they're dying out, but I don't think they're going to be completely lost for some time. I think they're a great starting place for people to find others with similar interests, and I think they're going to be around for a while. They're not easy to start up, hence why I think things like Facebook groups and Discord are kicking off because those are pretty quick and simple to use and start up, whereas a forum takes time. Plus Facebook groups and Discord allow for instant responses whereas you may have to wait with a forum for a response.
Forums are dying so spare yourself the pain of the slow and inevitable death of your forum. Close your forum now and just post on the ones left until they're gone too. 😛 Just kidding, but yeah, nothing lasts forever.