It's pretty easy to differentiate from a powershortage and someone yelling "PLEASE KILL ME" and leaving.
As for the abusing part, some cases like the one i just had are pretty obvious and should imo instantly be rewarded with a month long ban. This isn't someone who get's angry and calls someone a bad name, this is just intentional trolling. Sure, you can have your teammates fake trolling but that should get them banned.
As for the effort it takes to scan all the games... The tribunal seems a pretty nice method for that. If it's able to punish offenders it can also support victims.
Edit: I also considered that it would encourage people to bully someone into leaving.. But again, you can see in chatlog when that happens, making it easy to punish. Tribunal should start differentiating greatly between someone who get's angry and call someone an a-hole and people who inentionally screw games over.
It's pretty hard to do it IN REAL TIME thou. Do you think that Riot wants to hire people that will sit there and read ALL CHAT LOGS of ALL GAMES in which a player disconnects just to be fast and click "loss prevented" before you end the game? It's hard. In fact, it's so hard to do it good that it is not a sense to do it at all.
And just please, take it like a man and stop cryin' around about one lose. If you're good enough, it won't make you stop getting higher division or shit. I got to plat I by coming straight from plat III and to plat III by going straight from plat IV. Then when In plat I i dropped back to plat II to get back to plat I the next day and the next day to get to diamond. If you are skillful enought one loss is not enough to stop you from going.