AFK system idea.

A player afks in your game say at the 25 minute mark. If the player who is afk is on your team, he only takes the lp loss a while you don't lose or gain any lp. For the enemy team they still gain lp from the game.

If the player who is afk is in a party with you, you also take the lp loss.

This should apply to all elo's but Master-Challenger