How Long Does It Take To Recover From A Medically Induced Coma?

Can someone who has been in a medically induced coma for a brain tumor treatment recover to where they were before the coma was induced? My friend is a 50 y/o male with a tumor in the brain that is malignant. He underwent cyber surgery, chemo, and radiation. As a second stage of treatment was put into a coma. What is the possibility of recovery to a pre-coma ability and cognition?