Glioblastoma is a very bad diagnosis. If he comes back it will be brief. Someone needs to talk some sense with him and implore him to retire gracefully.
I've had glioblastoma take friends. In my experience, he will be bedridden and surviving on morphine in 2 months, dead in 4 months.
Someone with Glioblastoma has, at the most, about a year and a half to live. It sends out microscopic offshoots throughout the brain that rapidly grow into tumors. It is the most aggressive of primary tumors of the brain for which no cure is available. Each extraction through radiation, causes damage to surrounding brain cells. Such treatments destroys brain function with dire consequences. It is a terrible way to go.
Prayers.
Never happen.