No, no it'll always have a fanbase because it's 1) Free and 2) Free with an established base. Even if LoL starts dying, it'll only lose the hardcore batch at the very most while the casuals who don't want to pay will hang on.
Although, if Valve ends up getting a much better community than LoL I can see it being the final tipping factor
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Eh? You Serious? Easy Mode? How Disgusting!
Only Elementary School Kids should play on Easy Mode.