The thoughtfulness of your friend's wife is the most important part of this story. The bow is such a non priortiy portion at this point in his grief of suffering the loss of his partner in life. Some day, though, he will be able to appreciate what she had you do for her and him. The time you spend helping him cope with life without her will mean far more than the actual shooting the bow ever will.
Don't forget to invite him over for supper, helping you around the house, picking up items from the lumber yard, anything to help him spend time with others who care about him instead of countless hours alone with no one to talk to. Sounds like you are that kind of friend.