It certainly is a good warning to people who are going on an extended vacation or cruise! I'm glad your parents got the dog back. I'm sure they must have felt terrible about the situation. The older answering machines did not have the ability to get messages from other locations. They did do a good job with what they knew to do.
Gracie has 2 phone numbers on her ID tag and her micro chip has three different contact people. This is the very reason I insist that she have an ID tag on. Many people who pick up a stray dog do not think of checking for a microchip.
It certainly is a quick and easy thing to get a new ID tag with the info of the people caring for your dog while you are gone. When leaving the country though I would also make sure that your microchip info has at least one additional contact person attached to it.
Your sister must really have great confidence in her dog and your parents. I think if I was away from home on a cruise I would be calling everyday to see how my baby was!
I usually have my daughter here to baby sit when I'm gone or I have someone else come to stay. Thankfully, I have never had to leave her anywhere else.