I would have to say that if he is going to be in pain...and more pain as he gets closer to the end then it would be better for both of you if you put him down before you left.
Watching a loved one suffer is not fun rather it be a pet or human. Personally if he is suffering and he was my pet I would put them down only to keep them from suffering. Going to heaven is a lot better then suffering in pain and you would rather have the loving memories of when he was healthy.
The final decision is yours and what you feel is the right things to do but to end his suffering I would consider it myself.. I am sorry you are going though this and pray things get easy for you...
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.