I have a couple brainstorming suggestions, I think people are looking at this at the wrong angle. You don't want to punish the average player, who is bound to ragequit/disconnect every so often, you want to go after the ones who abuse it. Since it's a computerized rating, there needs to be a way to correct it when it's information badly represents a player.
1) Allow the losing team to "Earn" as much favor as the winning team (Opposing teams average). The winning team would get their usual values. The losing team would get a percentage based on how many kills, captures, damage, match time, and other such stats. If they fight hard to the bitter end, they'd get just a little under the opposing team.
2) Spend favor to reduce your ragequit rating. After all, if these people legitimately disconnected, you can assume they also have frequently played games where they didn't.
3) Reduce the disconnect rating every time someone completes a game with a loss.
4) You get a demerit for the day, if you get too many (Say 7-10) you are visually red flagged for frequent disconnects. Hovering over the flag shows the total disconnects.
5) Reward people for being a good sport, maybe whenever someone manages 100% of favor from idea 1 when losing gets a special green flag for the day.
One more point that has not been brought up: Occassionally, good sports on the other team may want to leave to even the teams, that person should not be punished.