I had trouble putting my dog down a few weeks ago because every time we scheduled the appointment he seemed better again. When he was feeling bad, it was really, really bad. I couldn't do enough to help him stop shaking in pain. He was a challenge to keep medicated, even the vet and staff agreed they hadn't had so much trouble before. But we worked on it every day until he had his dose, and then I had to double his dose. The night before his morning appointment to be put down, he felt better again. He slept peacefully for a change cuddled next to me all night, had a big juicy breakfast of his favorite meats, and ran around outside. When we got to the vets office he was so excited to sniff and bounce around in the grass outside, wagging his tail at the other dogs. It was heart-rending to go ahead with the appointment, but I kept reminding myself of how inconsolable he was most days.
I really don't know if he could have had more good days, but I do know if he had more bad days because of my wish to hold on to him, that would have been my fault.
Sorry, this is probably no help at all.