we currently have the IF archive to keep sourcecode and game files, and IFDB to keep track of games. this goes back some number of years (the 90s I think). I’d say the state of IF preservation is pretty decent in that sense. In general, the IFTF has made it a mission to conserve a lot of things.
there are past discussions about IF that haven’t fully been preserved due to net/link rot and the community hopping from platform to platform, but I think a lot of stuff did get imported onto Discourse (this forum software) so even a lot of that’s preserved. The gaps, imo, are some lost games from the past and, I’d say, whatever’s going on in the tumblr twine scene, since that’s a world that’s seen as separate from this sphere (intfiction forums, ifdb, etc) but is also IF. the nature of the blogging platform makes it harder to keep track of things, and I don’t think most of those people have their games on ifdb. @manonamora iirc has a blog that collects them though.