I had this same experience recently when I moved from New Orleans back to Vegas. I had a beautiful and sweet husky hybrid named Sasha. Unfortunately, I had to leave her with my brother so it was considerably easier than having to give her to a stranger. She was my constant companion for three and a half years (some of the most difficult years of my life) and it broke my heart to have to give her up. I worry about her almost every day and wonder if my sudden disappearance hurt the dog as much as it affected me. I really hope not. I don’t know what your circumstances were, but sometimes we have to make difficult decisions in life. To bluntly answer your question, I would never put an animal down unless there was no other option and I sincerely believed that it was more beneficial to them i.e. their suffering was so unbearable that death was mercy.