I was faced with a similar situation several years back. My mom's Scottie Fala was so sick, she had to carry her out to potty or just change her sheets several times a day. Mom had to go on vacation that was already paid for and had asked me to pet-sit Fala and the cats.

I knew that when I got in and after she had left, I would take the poor dog to be PTS. I fully expected her to not talk to me for years, but the dog was miserable. But I did not tell her this. Anyway, she had already had Fala PTS when I arrived the day before her departure. She had difficulty with the concept of mercy and euthanasia; it's a Catholic thing. Anyway, her excuse was that she couldn't leave that for me and that Fala was her responsibility.

I think that vacations can be refunded or rescheduled for the death of a close family member, esp if you have insurance. Sadly a family pet probably does not count as a family member.