saw this post today "Do you want to get your dog to or from the US? Puerto Vallarta Pet Transporter is here to help! We provide ground transportation to the US for dogs and cats. Our trips are safe, fun, and we treat your pet as our own. We currently have a sale on northbound trips to fill our last remaining summer spots. Don’t delay!"
It sounds as though they have been trying to find some other solution. Shipping an animal - especially in summer - has gotten much more difficult in the last few years.
I have been a volunteer for shelters and breed rescue for more than 30 years. I have seen older animals placed in new homes who adapted beautifully. It is not a perfect solution by any means but it can work. I hope you can find a satisfactory solution for you and your dog.