It's 2016 4v5's are still a plague to this game.
To start I'm going to negate the idiotic counter arguments against changing how 4v5's are dealt with.
Firstly. /mute or [TAB] click mute icon. There is no excuse not to use these functions if you think you are being bullied by a teammate.
LP Losses: The leaver takes the team's full lp hit. If the leaver has friends/premade in the game they share the teams full LP hit 60-40, the 40 is then split among the other friends/premade in the game.
Series games: If a player is the victim of a 4v5 in a series game and not friends/premade with the leaver the loss shall be forgiven and the series will revert back to before the game.
It's time to start addressing the real toxic aspects of this game. Until punishments match actions players will continue to afk doing much more damage to the game than any words could, especially with the /mute function.
Instant, month long account & ip bans for players who afk in ranked games.
Implement that and watch the afk's drop like a special snowflake jumping off a bridge.