I agree with warrior why should someone be forced to leave a game they started??? It's not fair to that player.
A better way of thinking about it, is if you have an afker or leaver, that has committed to the game for > then 15 minutes. And you end up losing the game because of it. Then the leaver should be forced to lose the entire 10-13 elo, While everyone else on the team still in game losses half that amount 5-8 elo. The only 2 problems i see with this, is people taking advantage of this system by purposely loggin out so rest team gets half elo loss. More likely to happen in duo ques, as solo que people want to be greedy. Another problem will be for riot to determine whether that team was actually winning before the person jumps out of game. Shouldn't be to hard, it can be worked out by gold. If the winning team is up by atleast 7.5k gold total ( which is extra 1.5k old per player) before someone on the team cs' or rage quits. That extra item should help win them the game. however with people getting better late game and other dying it's hard to tell for riot. But there would be a point where people are very hard to manage. I.e. team up by 15k gold before dcer. Then end up losing team fights cause of blitz pull making it 3v5 sort of thing. Thats my 2 cents.