He'll be dead in a year.
That's a bit extreme. He has already under one round of chemotherapy, and is to be treated by an oncologist who is board-certified in radiation therapy, and has indicated he may undergo radiation therapy and/or immunotherapy. Yes, he might be dead within a year, but it's far from certain, and more chemotherapy wouldn't be a guarantee either, especially since he had an especially bad reaction to it the first time. Quality of life matters, and it's not clear that he won't get more of that by going his chosen route, even though he'd very likely get more quantity of life with the chemotherapy.
I hope not. I can say that from what I've read about chemotherapy, I wouldn't personally take it for myself, either.
Just watch my 23 year old child die in 6 months after 26 days of radiation and 4 rounds of chemotherapy. I'd say in 6 months time he had a total of two weeks where he felt really good.
I'm all for the kid choosing a higher quality of life for however long his life will be-- and avoiding another round of chemo. It's barbarism.