My dad also has stage IV squamous cell carcinoma. Diagnosed late last year. He had radiation and it went away, then some months later it was back and had spread to his lungs. He's 78.
He's now on i/v chemotherapy fortnightly (not sure of the drugs), and getting a good response with the spots on his lungs shrinking.
He claims he feels perfectly fine, no side effects from the chemo. He spent five hours doing my lawns and garden last week. And no I didn't ask him, I came home and it was done and I felt terribly guilty!
He lost quite a bit of weight at first, but has put it back on.
After his current protocol, his oncologist has suggested he may go on an experimental drug treatment. Again, I can't tell you the one, he never knows and gets annoyed if you ask him too many questions.
We are resigned to him being on constant treatment until it impacts his quality of life, and then he decides what he does. There are counsellors and staff equipped to advise in most oncology units.
Obviously your dad's existing conditions will complicate matters, but mine is feeling pretty good at the moment, about eight months since diagnosis.