You can ask for a second opinion.

You can ask for trials available. You can ask the doctor why he has been dischargerd. You can also ask the pallative nurse. 

If you feel your dad wants more treatment and you have discussed it with him then start asking questions asap

My mum 10 years ago had lung cancer in one of her lungs. She was told nothing they could do basically go home enjoy your short life.

My sister friends mum had same thing got a second opinion went to another hospital had bottom of lung removed some chemo and is on tablets for rest of her life. She still lives till this day. 

Just saying always have hope until there is none. And dont just accept the doctors words get all the info and listen to what your gut tells you. 

you get answers

My husband was discharged from the oncology dept in November last year because there was no more treatment on offer. He has cancer of the duodenum. Since then he has had no contact at all from his GP or Macmillan nurse. Had helpful visits from local hospice nurse before Christmas, but as we are coping at the moment, there are no more visits. My hubby will not contact anyone himself and would be angry if I did so on his behalf. There may be things that could be done to relieve some of his symptoms, but he just wants to be left alone. 
 

I was having support from the hospice but this had to stop when we went into lockdown. I feel very isolated and feel that everyone has forgotten about us. My husband has already lived 6 months longer than predicted, but this form of cancer is rare, so maybe they don't know how long sufferers can survive. Feeling pretty desperate at the moment.