I've run into people like this more times than I can count. It honestly seems like LeaveBuster is simply there for show. Because 6 ranked games in a row I've had an AFKer/DCer. -- And if it DOES work? The consequences are obviously so minuscule, nobody gives a damn about leaving a game or thinking twice before doing ranked before checking to make sure their internet connection is decent enough.
It just doesn't hurt them but everyone else in their team and we have no control over this. We're doomed to suffer trolls/ragers/DCers because I have yet to see any REAL progress made to make Solo Q a more friendly/efficient system.
I've lost out on being Gold+ so many times because of this, as have many other of my friends and people I've talked to in Solo Q. I really wish Riot would focus a lot of their attention/resources on this major flaw. Because ranked is FAR from being passable. - Honestly it's best to just do Team 5v5 if you can.
Best of luck to you man, and sorry to hear about your game.