I might get downvoted a lot, but I am just going to add my 2 cents to this discussion constructively:
I would agree with a 24 hour ban if, and only** IF**, Riot can determine the status of the player, whether it be AFK or simply has left the game.
If someone's game is not lauching for some reasons (DirectX unknown error comes to mind), internet crashing, power going off, etc. how do you manage that? How can you actually make sure the player has left the game/went AFK?
Don't get me wrong, I have been there, I have lost games to people going AFK and stuff, but yesterday I got my first game crash in YEARS and I left my friend solo ADC bottom lane while I spent near 35 mins patching the game, trying to reconnect. I got reported, had to click the "I agree" button stating I was not going to leave... Even though it was not my fault at all...
TL;DR: Yes for a 24 hours ban, ONLY if Riot finds a way to make a difference between a game crash and an actual on-puprpose AFKing/leaving player.