Well, that would not be a very good idea if your making a high end game, oh just tell all the customers to download OpenGL? Or illegally force them to download it.(Not trying to offend you, I apologize if I do).
oh just tell all the customers to download OpenGL?
Pretty much all commercially available games expect either OpenGL or DirectX to be installed on whatever computer they're running on. It's written in the "system requirements" section.
Or illegally force them to download it.
There's nothing illegal about it.
OpenGL is available for download for free. In fact I'm surprised your friend doesn't already have it installed... very few people have to manually download and install it because it's often bundled with the OS and/or video drivers.