I can only imagine how hard of decision it is to make to put the beloved animal down because there is no hope. I do understand it's necessary in some situations, but it's just very hard.
Hardest decision there is. I made that choice in July to say goodbye to my Hannah Banana. She was my 16 year old german shorthair. I got her as a puppy when I was in high school. I miss her like crazy. The toughest part has been helping my kiddo cope with it. Just the other day she said "Mommy I really miss Hannah, who am I going to share my extra french fries with?"
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.