While banning an AFK player after a game potentially prevents future disasters, many features could be created to help make LoL a more balanced and fun game when and if a player does go AFK. (which really is the worst, especially in Ranked)
Here are my suggestions (please include yours too and hopefully Rito might be interested in something like them)
A) Stronger minions in all lanes to siege the towers and hold back the enemy to make up for the lack of a player (constant Baron buff plz)
B) Towers could have increased health, be more aggressive and do more damage. This may help prevent the all too familiar tower dive that will inevitably happen when the enemy team's bored extra team member will now be roaming the map free farming kills.
C) Have an insane bot take the AFK players place, keeping in mind the A.I will have to be programmed damn well so that the other team doesn't just farm this bot for gold (in fact don't have that bot give any gold for killing it) Let it be a spooky ghost or something (tie it into your lore, whatevs: make it Lucian's wife idk)
D) Kills on the AFK teams side should give MUCH less gold, same goes for towers OR Kills done by the AFK side should give much more gold
Honestly Rito just do something, we are suffering out there. If you don't have game designers in-house who can solve this problem, then hire me :D my rates are modest and I spent like 5 minutes coming up with these ideas (you can have them for free btw :D)