I'm so sorry about Angus. Please do not speculate on what would have happened. You did the right thing. Seeing Angus in that condition, I would have done the same thing. At least he was with his family at the end. You have good memories of him "deciding" to like you towards the end and you have to, no MUST take those sweet memories with you.
Thank you for sharing his lovely picture. He was a handsome boy. You did the right thing, remember, he is now safe and healthy and happy. And I will repeat for the 1000th time here on PT, that my RB Cody is the "Watcher over the Bridge", a high honor, so he will take care of Angus. God Speed, Angus, play well.