I must say, I was somewhat dissapointed. The game seems to present itself as exploring the concept of dead online servers and the eerie feeling they give, but quickly ditchs that in favor of a creepypasta-tier "loved one inside the cartridge" story and surprise ARG that I wasn't pleased to discover was mandatory to get the real ending.
But there WERE options to get the ending or not. [1] You can leave the game like the "JOHN_DEV" guy told you to or [2] You can capture and return the flag, ending the game.
Another option to get the ending is [1] Shoot the gramophone and continue getting stalked by some ghostly being or [2] Don't shoot the gramophone and continue exploring the arena