I have been playing league for many years, I know this is a long shot but it's an idea I have had for a long time and think it would be so good to have in the game. This idea will allow you at riot to know for sure whether the player is disconnected or AFK, this can be done by very simply making players do a (Pre Game Ping Test). if the player does not meet the recommended ping set by you at Riot the player should not be allowed to play. This will let you know when people are genuinely AFK in a game and then the right penalty can be issued by you.
Please just try it in the PBE to start with and see how it goes. This would change this game for the better. AKF's are unavoidable but DC's can be avoided.