Yes. I just added it. You can find it here: The game view and playing games · online-go/online-go.com Wiki · GitHub…
It is not OK to just “leave” a game, by closing the browser tab or letting the game time out. It is also not OK to stall games in any way such as with pointless moves or endless resumptions of play.
Previously (and still) covered by the Terms of Service as a disruptive behavior and while the ToS, may not be very clear (Like most ToS), I think we can safely say that it is reasonable to expect that a user should realise that such behavior is unacceptable unless they forget that there is another human being on the other end of their game.