Special "kidney diets" are nothing but garbage,read the label,is it any wonder your dog won't eat it.
My Firbi developed kidney disease as a 12'5 year old. On the Vet's recommendation we bought Hill's but after one meal, there was no way he would eat it and in the end the Vet told us to give him whatever he WOULD eat because we shouldn't let him starve. So we gave him raw food with his normal diet and took care that he maintained his weight. More, smaller, meals each day helped too.
We had him with us for about 6 months after the initial diagnosis but in the end he just gave up and I had to call the vet and go down the garden with a spade. Our Vet comes to the house. I would never send a dog on that last lonely journey among strangers. They breathe their last at home, in my arms and are buried here in the garden.