Simple logic to show how much effect an AFK can have
89 points in ranked, win one more game to promo
Score is 9 - 5 in game, advantage in tower and dragon
Teammate leaves(ADC), follow by losing the current game, which in term also loses me getting to promo
Next four games: Win, lose, Win, lose.
If I was in Promo I would've been in next division and I would not have been demoted cause I've just got to the next division with 0 points.
But instead, thanks to that AFK I was stuck in the same division and pretty much gained nothing.
I hate how AFK is part of ranked, it's not optional, something you HAVE TO deal with if you want to play the game.