I am not altogether happy with your presentation of chemotherapy as a "just in case" measure, nor as a "palliative which ignores its terrible effects".
My experience (with at least 25 individuals over the past 15 years) has been that the medical profession does not always administer it as a cure for cancer, but rather in order to obtain remission in terminal cases which offers a better quality of life up to the point when the cancer reasserts itself, at which time the terminal episode is greatly shortened, making it possible to control the pain.
In earlier decades, pain control had to be administered at an earlier stage and suffering often became uncontrollable as an agonizing death grew nearer, unless, by holding back pain control in the earlier stages, the last few weeks could be made "more comfortable". In any case, the symptoms of drug addiction took over before the end.
I happen to know of quite a few cases of terminal cancer in various organs of the body (which you list as unsuitable for chemotherapy) where in a remission of anything from two to five years (in one case 13 years) a normal independent life with only minor side effects followed the trauma of chemotherapy and was in turned followed by 10-30 days rapid deterioration into a peaceful death because pain control did not cease to be effective in so short a time. Beryl Shedden, Church Stetton, Shropshire.......