OR another suggestion - "flag" ID's that do not finish a game (in 30 or 60 days), and in the rating list - have 3 different settings.

Provisional - established - active (with active just being the people who had finished a game within the last 30 or 60 days)

That way if a player takes a vaacation, or takes a break from the games, he will not lose nothing plus his "true" ratng can still be seen.