Nay, I say! But I can understand why most think it would be dead at this point.
1. The game started late into the system's lifespan, so not much would've been added to it like the others. Plus it's a new genre for Nintendo, and they don't have another game like it so some might get bored really quickly and go onto another game.
2. Splatfests have officially ended, and it's the reason why most even played the game to begin with. That, and the Snail Shells are basically gone. So a lot have lost interest, but the few who enjoy it outside of the big events will stay as long as the servors will be on. After all, the game has a huge thing for multiplayer and it can be played at any time. I just hope they add more to 'Splatoon 2' in the future, and expand on everything that was in the first (just PLEASE no handheld version!).
3. School just started for a lot of people, so they have less time to play. Then there are those who have actual jobs. This is probably a big reason along with the 2nd one.