Offer Bot game to 'guest players'. Enable people visiting the log in page to play a bot game without having to register or log in.
By giving the opportunity to try before you buy, I think it will attract more players to the game. Personally I don't join sites that I have to give e-mail address etc, before I know what i'm joining.
The game page could include notifications such as 'join now for free access to more maps etc'
There would be no need to archive games, it would not effect any existing players scores, rank etc
Its would benefit the sight in many ways, It would allow prospective new players to check out the game play before signing up. Prospective players would have the opportunity to play a speed type game. Which in its self would encourage new players, more freemiums = more premiums.
“Do not spoil what you have by desiring what you have not; remember that what you now have was once among the things you only hoped for." (Epicurus (Greek philosopher, BC 341-270))