If the Fellowship is sundered from Parth Galen, I'm quite sure Gandalf would be with the 4 hobbits going to Mordor (possibly Gimli will be with them...remember his statement before they left Rivendell?), and they would not be taking the path of Cirith Ungol, considering his reaction upon knowing Frodo and Sam's path from Faramir. But where would they pass through? Morannon?