Baldness can be prevented with fasting followed by better diet and better lifestyle.
It is a prevention, but not a cure all.
Once you have lost hair, and once your hair follicles are gone for good (happens often with some autoimmune diseases), it is generally too late.
But hair that just falls off during fast usually grows back like any other hair. Every day we loose from 20-150 hairs naturally, and usually, as many grow back.
It is almost like if you cut away your arm.
You can not regrow new bones and new organs, not even while fasting.