Vicky1,
Depression, and even suicide is a major factor with head and neck cancer patients. I once read as far as cancers, suicide was 5th with Head and Neck Cancer patients, but recently read it’s second behind pancreas cancer, but regardless, all threats should be taken seriously. Maybe your father can see a therapist, talk to a friend or minimum tell his doctors!
Some anti-depression medications can even cause these thoughts with certain individuals with no history of this or even with this disease, it did with me. I contemplated this, still have a wrist scar, but attempted several times, other ways, which was all I thought about doing when I was hospitalized for 6 months in 2010, and paralyzed from the waist down or was just so weakened, with no good prognosis. The hospital and staff had no idea either! I told one friend who came to see me, who had convinced me that if i wasn’t successful, I could be permanently harmed, disfigured or paralyzed. That made me think, so at one point, I requested the hospital stop giving me anti-depression meds (only do this by dr request), but I don’t know if this was the cause or not, but haven't had this problem again, even after multiple cancers, but here I am still, cancer free, 9 years later.