I'm so sorry for your loss. We went through this same thing with one of our dogs many years ago. We were fortunate, as the steroids did their job and he recovered.
From the photo of Potsie, I can see that he was well cared for and obviously loved by you very much. After going through the abuse, it's wonderful that you had him and showed him a great life for the time you had him.
And looking at it from Potsie's point of view -- you were strong enough to let him go and end his suffering. If he was still with the abusers, he could have had a very painful, lingering end.
Bless you for rescuing him and giving him the best time of his life, in the time he was with you.