I will tell you what I did but I must stress quite strongly that I am no vet and I did the best I could with what I believe was right. Not everyone would agree.
My Whippet was diagnosed with kidney failure, I want to say 2 years/18 months ago but I cannot remember the exact time line. All her life she had been fed Lily's Kitchen organic with extra toppings of salmon, chicken, beef, veggies (not popular), homemade stock and leftovers. She was never interested in food and when we had her as a lone dog we could leave the food out all day, she would just pick at it.
When she was diagnosed I moved to Hill's Renal diet both kibbles and wet. She would never eat the wet food and would only eat the kibbles if mixed in home cooked food. I tried to removed the home cooked food entirely but she just would not eat. I then took the view that if I was her age with what is in effect a terminal disease, I would rather continue with gin and pastries and probably would take up smoking again because why the hell not. I would rather shorten my life a little and have fun in the meantime. So I resumed mixing her favourite foods (mostly lots of homemade chicken stock, chicken and cheese). We continued like this for some time. One vet I saw agreed because I think there was not much more to do.
Three weeks before she was put down she stopped eating entirely. The vet gave me meds to make her hungry but she was losing her marbles (it was miserable seeing her eating like that), became even more incontinent and would refuse to get out of bed. The bloods showed an issue with liver on top of kidney and they recommended more drugs to make her eat, a stay in hospital to bring fluids up (but this would have to be regular trips and she was terrified, I mean properly terrified of the vet) and more investigation into the liver problem. She was about to turn 15 and I thought if it was me, I would not want to live like that. The vet also thought she was in pain.
I take some comfort in knowing that the last few months of her life continued just like she had lived and that all good things come to an end.
I don't mean to sound gloom but just share our story in the hope that it helps. For some things, there is only so much medicine can help with and we need to decide what we are comfortable with.