I am blind in my left eye. It was the result of an accident when I was 10 years old. You adjust in ways you do not realize at first, but with awareness you begin to understand the different methods which help you navigate. IMO the biggest challenge in golf is putting. Years ago I developed a putting style which was similar to a hockey stroke, but was most effective by anchoring the putter to my left side. I altered the putter set up to accommodate an open stance (45*) which allowed me to see well past the 6-7 foot sight restriction with a square stance and the stroke I could repeat effectively. I sold over 600 putters with this set up on ebay prior to the anchoring rule. Most of the sales were to golfers that were right eye dominant or left eye if they were lefties. An open stance allows everyone to see the putt much more clearly, but a traditional putter is not set up well for a stance which is so open. Now I am working on adjustments to my putter to accommodate the same set up without anchoring. I have settled on what works best for me. Now my goal is to resume my putter sales this spring as it has always been for me, a hobby business. Encourage your friend to learn to read a putt with his feet. It is difficult to read greens without depth perception, but if he will work at walking the line of his putts on both sides of the line he will find with a bit of practice you can become effective in reading greens. You have to work at this and evaluate all your "reads" to be effective.
I will add that with the full stroke or even chipping, etc. your friend will be successful in golf if he develops the habit of picking a spot inside of 6 ft. when he aligns full shots. My experience has me picking a spot on my line from behind the ball. Keeping that spot in my sight as I move to the address position and then focusing on the spot with my full stroke. I find my best approach is a spot about 5' in front of the ball for the driver, 4' for fairway woods, 2'-3' for medium irons and wedges, and 1' for pitching and chipping. This will also help him to make a better shift because he will find without sight on the left side he will tend to hang back through the shot.
A PS to the above. It took me a while to realize that with one eye you don't line up well when you square your body to your line of sight. You will tend to set to the middle of your body and create an error in alignment. You need to move to the side of your vision (with your feet and not just shifting your head) making your good eye your point of center and then you will be spot on in reading your line. It seems simple and should be self apparent, but I still have to remind my self to do this in golf, etc., even though at 76 I have lived with this limitation 66 years.