I think he is already on his way to doing so since he is still fairly young and has been "clean" for several years and he is now aware of the "alternative" methods of good health.
It is my understanding that the liver is the organ that will regenerate itself as long as there is some healthy portion left.
And even though cirrosis (which he probably does not have) is a condition that cannot be reversed due to scarring of the liver, I understand that we can live with only a portion of the liver being healthy.
I hope this eases your mind a bit. I am no expert but I believe in a Higher Power and a positive attitude. I know from your posts that you feel the same way. Your son-in-law is being healed now!