I've heard people talk about backing up the entire DT Wiki. There's some (very Wikipedia…) bickering about image rights and such, but, technologically wikis do seem to be more backup friendly than forums.
The Great Finds thread, Matteo's projects, Soarer's, Hasu's, classic group buys and the like are not as obviously saveable. I've found a spot of bit-rot throughout the DT forum, a problem going back many years (to at least Matteo's user interface transition), but searching for examples just now keeps on turning up black holes on GH! They definitely lost a lot more over the years than we did.
Here's a DT example: try following the link in my 2016 post here. I made a restoration/photo thread for the German layout beamspring I bought from the Rustmeister a year or two before that, but it was all gone. Similar story for some of the DT Awards photo contests. I recall using Archive.org to dig up those pics when they came to mind to post again. But that's a very manual process, mostly done by my own memory of where things once were. Not exactly the open web!