Just a quick idea, don't know if it would be practicable: maybe a "thread move announcement" thread somewhere in the site announcements would make sense and help people find things again (or safe them a fruitless search all through the forums, in case it has been made inaccessible for some reason). I have to admit that, in the short time I'm an active forum member, I've also experienced the bewilderment when a thread suddenly wasn't where I had seen it only five minutes before --- yes, I found them all again in a different subforum.