Even though my right eye is not totally blind, it is extremely impaired. Tell your friend to learn how to listen and catalogue traffic sounds. Compensate for the narrowed field of vision by looking further ahead, then learn how to anticipate developing hazards up ahead. Most of all, tell him to relax, he'll be ok.

Just a couple of footnotes here:

My right ear is more sensitive than my left ear, possibly to compensate for my impaired vision on that side.

I rely heavily on all three of my car mirrors when driving. Yet, I don't feel the need for mirrors on my bike. Probably because I can hear what's going on around me. As I am writing this I realize that I'd be very uncomfortable riding a bike if I was deaf.