That'll be reasonable but these games weren't.
The underage character(s) can have been introduced in between the last time you played, and now that you search again for the game. Another possibility is that the game goes full online only. But, to my knowledge, those are the only reasons why a game can be removed.
I mean, there's even threads for 0.01 version abandoned five years ago, so no, a thread do not disappear without suddenly going against the rules. Even the fact that the game wouldn't anymore be translated in English wouldn't lead to the thread be removed. It will not be updated anymore, but the thread would stay.