Most cat shelters have separate rooms to house a cat that tested positive. There are also false positives, so often the test is re-done. A perfectly healthy cat that tests positive can live a long time without ever displaying symptoms of the disease.
PetSmart should have explained this to you and what other options you have before agreeing to their outdated mode of dealing with cats that test positive. At the least they could have given you the option to take him back if he tests positive.
When der Brucer and I first took in JJ, it was clear in our minds that we would first try to foster him, and not adopt. We wanted to find the original owners, which is why we posted pictures of JJ in places where those owners could see them, with contact information.
Barring that, we wanted to find a home for him, preferably
not ours. Integrating JJ into our house, which has four very active and inquisitive dogs already living in it, would have been highly difficult, and JJ was clearly not interested in that option.
I need to make something clear here: PetSmart IS NOT the adoption group - the company
assists in placing the cats.
That euthanasia would be an option didn't even come into the picture until this morning, when the representative of the adoption group explained it to us. He specifically asked us if we would want JJ back if he tested positive. He made it clear that, if the test was positive, the only two options were that we take JJ back, or JJ would have to be put down - they do not have the resources to do otherwise. Der Brucer and I considered this option, and realized that it was not a good one for JJ or ourselves. WE were the ones who agreed to the euthanasia option, IF the cat tests positive (and that is, frankly, an if, not a done deal).