If you notice, when you play the game, the tracks of the Subway always lean towards the left and the direction of the tracks never changes. So, I believe the Subway Surfer will never stop running because he is running in circles so, the game will never reach an end.

Subway Surfers is an endless runner mobile game, which means it doesn't have a specific ending. The goal is to run as far as possible while avoiding obstacles and collecting coins.