As I struggled with my internet connection the other day I came to a realization. It is a LOT more frustrating for the person who is AFK than it is for the team. Abandoning your team, losing LP, and possibly being banned for factors beyond your control is one of the most annoying things about league. If you want to do something petition Riot to make reconnecting easier. I'm tired of having to ctrl+alt+del when I get the smallest hickup in my internet connection and having to completely restart my client to get league to recognize that yes, it does currently have a stable connection.
Either way, I very much doubt when you're winning a game, I very much doubt the guy who is doing well suddenly disconnecting during a teamfight is doing it intentionally.
Maybe if there was a way for the team with a DC to vote(or it automatically give you) a 2 minute time-out to give the DC time to get back into the game, if he doesn't reconnect in that time then you have to play 4v5, but if he is only gone for 2 minutes he doesn't come back 2-3 levels behind and have to play catch-up.