I have seen a couple of threads so far about people who loses 50 games in a row as a disco nunu etc. and STILL are not being banned (even after manual report).
I came up with an idea where the system would automatically send a report with the summoner's name to one of the appointed Rioter, when the account meets it 10th lose in a row. The Riot employee would take a look on his game history then and try to find out, if the player is just bad af or he trolls purposely.
I know it still wouldn't solve the problem, but i'm pretty sure a couple of them would be caught.