Outrageous!

People should get a foster parent if there is any chance they might change their minds.

We had a similar experience a few years ago. The family was leaving Canada to go and live Israel and live on a kibbutz for an indefinite amount of time. They wanted someone to adopt their small black cat. We did. Six months later they came back, having changed their minds about life on a kibbutz. The called and told us they wanted the cat back. We said no. We had invested time and vet costs and had successfully integrated the kitty into the household.

They persecuted us for over a year, finally playing the shrink card. They got her shrink to call us to persuade us that keeping the cat was going to cause the woman terrible stress. With all our neighbours supporting us, and ready to jump them if they showed up, we still refused and finally they gave up.