My doggie just got put down a couple weeks ago. She was 15... severely arthritic, blind in one eye, incontinent, completely deaf. She ate very little and had lost something like 7 pounds out of only 42 in her last months alive.
She was SO HAPPY and whenever I would come home, she would play like she was a baby again!! Since she was deaf, she would bark like crazy when she got excited, and never stop, so I would start tossing her fluffy christmas toy across the room, and off we'd go on a rowdy rendition of fetch.
She fell a lot, and slept most of the time, and wouldn't really eat, and had terrible separation anxiety - she would not let you out of her sight when she was awake.
Over the summer on her birthday, we made her a steak and a peanut butter dog cake, and put a pretty flower lei around her neck. It was awesome.
She had so much life in her... until one day, my Dad called me at 9 am and told me she couldn't get up. I went to see her, and she was dead in the eyes. She couldn't wag her tail. She couldn't make a sound. She couldn't drink anything (but we got her to rally for biscuits and celery). It was heartbreaking. She got so excited when she got in the car... she loved those rides.
RIP Lady
Anyway, we KNEW it was time. If your pup has life inside, let your pup live with that life!!
We didn't have a vacation planned. If you don't think your aunt and uncle are good caretakers, then find someone else. The dog shouldn't have to pay for your family members' irresponsibility.