This is available, but not intuitive.
A player may choose to disconnect from a game. There are warnings all over the place about how doing so will affect your rating, and causes many players to never click that option. However, when one does, several options are presented:
Disconnect with penalty. The game may try to play on without you, nobody gets any ELO rating, and you get a big "this player disconnects" added to your profile and table information. This is what most people think is the only option.
However, there is also:
Concede the game. You lose. I'm not sure what happens in a game with more than 2 people, but in a 2 player game it ends, you lose, and the other player wins. ELO rating changes as if the game had played out, and no disconnect penalty is given.
Collectively abandon the game: Nobody wins or loses. However, all players must agree to it. ELO rating does not change, and no disconnect penalty is given.
There may be one or two other options, I don't remember for sure.