ANSWER:

This is a major sin. 

If he believes in it, it takes him out of the fold of islam.

My question is that if a Muslim plays a video that has Shirk in it, then does he loose his Imaan? The Muslim hates the Shirk and Kufr in his heart tremendously in the scenario but he plays the video games. In one scene, he is with the Hindus in the temple where he has to engage in shirk, otherwise he cannot proceed. He only plays the game for the shooting and adventure.