What happens if M-shaped hair loss progresses?

I have a friend whose M-shaped hair loss is gradually progressing. Originally, men say that it happens little by little. He used to take medication but now he is not taking it anymore. The medication only slows down the progression but cannot stop it. What I am curious about is, as it progresses like that, does it lead to complete baldness as we usually understand it? Or is M-shaped hair loss only a slight thinning of hair at the front? If it worsens later on, will all the hair eventually disappear?