Keep checking with the Planning & Development Department just in case the neighbors try to get the alley closed/vacated. The Department should inform all of the neighbors anyway since at least 2/3 of the neighbors would have to agree by signing a petition. But sometimes these matters have a way of slipping through the cracks. So it's probably in your best interest to monitor the situation yourself.

As far as the petition. Andy is right. It not going to hurt to have someone sign a petition. In fact, it would probably help to show that you have support in the area, especially in an election year. Good luck.