Im very sorry you had to experience all of that. Im am a huge animal lover and I know how it feels to have something happen that could have been avoided. I had a family dog several years ago, and we were celebrating my sisters graduation. We drove to my grandparents house and my parent brought our dog in their van. After hanging out several hours later i started to wonder where our dog was. It is a large farm and we thought the honey was playing with the other dogs. Once I said something to my parents, we all stopped, looked at each other, and ran to the car. My dad pulled open the door, and pulled out our dog already in rigamortis. All I could see over the car was my dogs legs standing in the air. It didnt take long for her to pass in the middle of June with 100 degree heat.
Everytime I think of that I cry and it took me a very long time to stop blaming myself and my parents. It doesnt get you anywhere and just causes more pain. You werent attached to this dog, so you can get over the incident and stop blaming yourself, and wont have all of the lingering feelings of a missed pet.
Im sorry if my story wasnt relevant, but as soon as I read your story I was upset and reminded of my dog.