How long can this game survive?

So League has been the most successful online multiplayer of all time. It's really fun. It's really not fun. It's really frustrating. It's incredibly enjoyable. It's everything a game could be.

Tons of credit to Riot for updating the game every 2 weeks, making new champs, new items, new objectives, fun mini-games, cool skins, and a great pro-play scene. There's also many streamers that are very fun to watch, that generates excitement to play the game more.

I wonder though... is there a point where this game, for example, has so many champs that it is impossible to balance? Some other new MOBA comes out that offers some relief from things people have been frustrated with in this game for so long? What kind of thing could "break" League to where it loses its huge player base?