Rengar leaves a game after 2 mins and after moving. i want my lp back

This is unfair, why do i get a loss when someone leaves before 3 mins and screws our entire team. Riot fix your system for afk's. This guy knew he was screwing our team over because he said "screw my promos I'm leaving". they should be able to track if someone leaves within the first 5 mins of the game no lp should be lost.