My FIL was diagnosed with Lung Cancer last January. He had chemotherapy , radiotherapy and immunotherapy . He was really unwell whilst undergoing treatment and after each scan after the treatment , there has been no improvement In his cancer instead it has progressed to his brain now . He has around 5/6 lesions on his brain and is on the Pallative care team now to manage his life and help him eat and do things for as long as he can. 
my question is how long can he go on for without treatment , he is only taking 8mg steroids dexamathasone to manage his symptoms and has no treatment in place as they have said he cannot have further treatment due to his weakness and condition