Although I had wished that the alternate ending was more true to the novel in which Anna is an evolved daylight vampire who helps capture Neville and brings him to the vampires. She then explains that the vampires are a new society amongst themselves and view Neville as a killer and ghostly legend. And then they execute him.
http://www.firstshowing.net/2008/03/05/must-watch-i-am-legends-original-ending-this-is-amazing/