I assumed Judith was still alive because with TV shows, no body = no death. And thought it was really weird how Rick and Carl both fell apart and started grieving right away after seeing the baby car seat. I was like, "wtf? Why don't you look around a bit and see if someone has her?"

But then I realized that even for a show like this, you probably can't show a baby being killed. So they did it off screen. This is the only time I would believe a character were dead without seeing a body, because I don't think they would be allowed to show a body. And honestly, it makes more sense for the show to kill off Judith then to try and keep integrating her into the story, especially as she gets bigger.