Rules for requesting removed/dead threads?

Welcome to the group!

There are a few reasons why a thread could have been removed, though we wouldn't be able to tell you specifically without knowing what you were looking for. But generally, threads are removed if 1) as you said, there was some kind rule/policy violation - most commonly this would be a duplicate post, though it could be other things, too, or 2) admins received a copyright takedown request from the creator, or 3) some forum cleanup was done and a thread was merged with another thread or otherwise corrected to be more accurate (for instance if a title was changed, then the URL will also change).

Though the fact that you were able to see an expired download link means that perhaps the thread you're referencing wasn't removed but is in the trash instead? If something is in the trash, you may request a mirror in the thread if you wish and tag the OP if they're still active in the group, though it can sometimes be more effective for visibility to post a new request in one of the request sections. Once a thread makes its way to the trash, folks are usually no longer monitoring it and it doesn't show up in the regular forum view without specifically searching for it.