It doesn't sound like you were at fault. It's not uncommon for dogs to die around that age. He could have had a stroke, heart attack, etc. The owners could have an autopsy done to find out for sure.
my in laws dog did that. they left for work in the morning and she was completely fine. jumping around (as much as an arthiritc 13 year old shepherd can) and happy. they get home from work 8 1/2 hours later and she was laying in her bed...dead. they had an autopsy done on her to see if she maybe ate something but turns out she just had a stroke and passed away. sometimes those things just happen.
Firstly, it doesn;t sound like you did anything wrong. So don't beat yourself up about this. Death is a strange thing. My grandparents on my father's side died within 24 hours of each other. He had been taken into hospital, and died unexpectedly even though he was sick. My grandmother did not know he had died. Yet next morning she passed away from a stroke! It was mysterious, almost as if she sensed it.
It could be something like the "twin" thing, when there is a bond so strong (yes, even between dogs) that it has profound effects like this especially as they were both getting old. 12 is a good age for that breed of dog.
You feel responsible because they were "in your care" for those few hours. Yet I know it was not your fault.
thank you so much for making me feel better. I just hope my neighbors would never believe that I would do anything to hurt an animal. I love animals , thats why I foster abused horses. thank you again