If you have a leaver who has been afk for longer than 5 minutes until the end of the game, the team with the afk only looses half as much lp in case they loose, and the enemy team only wins half as much lp. (if enemy looses however they loose the normal amount and if the team with the afk wins they gain the normal amount)
If you have an afk who has left 10 minutes or more, before the game ended, you get 0 lp for loss and normal lp for win, and if you are in the opponents team you gain half lp for win and loose full amount for loss.
The premade of the afk is excluded from this,
and if the afk hasn't filed a bug splat then he looses 3x what he would have lost
If Riot can later definitively say that the bug report was fake then the player automatically drops 2 divisions from his current rank.
Thank you for taking the time to read this,
I would appreciate hearing your opinions in the comments