TwilitlordIt doesn't hurt that Riot is pouring money into League invitationals and tournaments and heavily promoting it constantly. If I remember right they're actually losing money even though they have the most popular game on the face of the Earth. While it probably won't get abandoned by them for a long, long time, I'm pretty sure that the day Riot stops putting money into tourneys is the same day the game begins to die.
They're losing money running LCS, relative to ad income and what not, but considering how much interest they garner in league by it being the most popular esport easily makes up for any money lost.