I almost had to do the same thing last year. My dog was diagnosed with lymphoma a few days before we were supposed to leave. I was ready to cancel, and had even emailed my awesome TA Tammy at KK asking her to cancel. Unfortunately, she went downhill so so fast that I had to send my baby girl to heaven before we were supposed to leave. We went anyway, and I spent the entire trip in tears. It was still better than being home in a lonely, quiet house though.
If I may ask, what has your pet been diagnosed with? I only ask because I've been in veterinary medicine for 10 years, and maybe I can offer some tips or ideas. You and your family have my deepest sympathies, and I will keep you all in my prayers. *virtual hug*