Urgent: Worried about a stray that was sent to Pound...

I was at a friend's house last night, and while we were sitting in the living room I heard cars honking outside, not a common thing in her area. I look out the window, and there's a dog in the middle of the road! So, being the dog lover I am, I ran outside and called the dog to me. She came with no complaint, and was very friendly. After looking her over and running her through some commands, I could tell that she was a pure-bred (or darn close to) Labrador Retriever, and very well trained. She had a collar, but no tags. My friend has two cats, and no interest in taking care of a dog. She told me to just leave the dog alone, and that it would find it's own way home. But I was too worried about it getting hit by a car, especially since by this point it was dark out, and she's a chocolate lab, not easy to see. I called everyplace I could think to call, but the only place open at 9pm on a Sunday was the local animal urgent car center. They told me to call the police. So I did, the cops came by, asked me to tie the dog up for the night and told me that they'd send the warden by in the morning to pick her up. Well, now I'm freaking out. Did I do the right thing? Someone has *got* to be missing such a wonderful dog, but I'm worried that I signed her death warrant! Should I call the warden and check up on her? Or just leave it be? If I lived in the area, I would have taken the dog till we found the owner... But I live almost two hours away! I've never dealt with a shelter before because every stray I've found, I've either kept until I found the owner, or adopted... Please help me out here...