The game can easily tell if you afk was intentional or not. There are two programs running when you are in game, so if the dc was not intentional riot would see that you lost connection to both the game and the launcher at the same time (They would be stupid not to have logs for this). If not then you it means you left intentionally and should be punished. Though if you end task both programs (starting with the launcher) it would look like connection issues and you might be able to get away with a couple more dcs then you normally would (I should really not give ideas to people).