yes I definitely would not take the cat. not only for the reason you stated but also because that is theft and YOU could get in trouble.

I think at this point you've taken the best first step you can. Wait to hear back from the shelter... if they don't have any advice then I'd call the SPCA or animal control if you have it. Other than that I don't know what else you could do other than maybe taking some food over every once in a while. but don't commit any crimes lol