My husband was diagosed with stage 4 bile duct cancer 1 year ago.  He had 7 cycles of Gemcitabine at which point the chemo had stopped worked and treatment was stopped due to COVID 19.  After a lot of shouting (we felt neglected) we finally got to see the consultant again yesterday and they are about to start active sympton control and a different chemo treatment (provided my husband feels well enough).  The consultant did not think my husband would be alive after 9 months but he proved them wrong.  Keeping going can be hard but what my husband had been wanting was to keep going on one treatment until a better one came along.  Macmillan are brilliant and you should have a nurse assigned to your Dad who you can always talk to.  I don't think that your Dad will be cast aside just because he decides he cannot cope with chemotherapy any longer.