I understand what your going through. Many of us have had the same situation with either a diabetic dog or an elderly dog.
Mine was a diabetic that lost his sight over time so he had time to adjust.
His biggest challenge I think was the RV steps and he did have some adjustments to make but he did, I believe that most dogs do with time, make those adjustments. I think it easier with the leash to help them up or down stairs that are steep on long, something like a two story building is a danger and the possibility of injury is much greater so I look at the leash as being necessary for your dogs safety.
I also would keep checking the Blood sugar levels, I found that when Zachery was under control with his blood sugar levels he did not drink any great amount of water so I have a feeling you may have a little more tweeking to do.
Good luck and please keep us posted on his progress.
Sher