Did we do the right thing?

[GailFrank]

I woud just like to hear other peoples views on what happened to us.
My beloved dog Bobby an 8.5 year old Jack Russell was put to sleep 3 weeks ago, he had a heart condition going back a while, heart murmur and an enlarged heart he was on medication for life.
4 weeks ago we noticed he was drinking excessively, we took him to the vets to be told he had diabetes, we were given a cd to study over the weekend on how to give him his insulin etc.
He started to vomit excessively over that weekend also, he just wanted a drink constantly but then was sick shortly after. The vet placed him on a drip on the Monday morning on collecting him we were told he had a secondary condition of Pancreatitis, he went to the vets and was on a drip for 4 days we took him home at night. He seemed okay for the first hour or so then started again wanting a drink and being sick.
He did not eat for 5 or 6 days.
On the Friday we rushed him in and told the vet he had been sick all night long. They said we could place him on the drip again but they thought he had had enough and was not responding to the drugs.
We decided to let him go.
My dilemma is could something else have been done?
I really miss him so, and I realise like minded people would understand my guilt.