Will League of Legends die one day?

Honestly, not a lot of "similar" game has died. You're not comparing it to the other MOBAs that failed, you're comparing it to the "Most popular games" before and after it. AoE, WoW, Runescape, Starcraft, DotA, Maplestory, etc all still have regularly active players. With tons of people looking for nostalgia nowadays, these once "Top" games still maintain dedicated playerbases that are not as big as they used to be, but are pretty loyal.