Glueball, of course you can make the left turn without the FMS. But previous and constant reporting over the past week stated that the left turn was programed into the FMS BEFORE the last voice transmission, the "Good night" transmission. That had tremendous implications that the intent to turn off course towards the west was established without the crew reporting anything out of the ordinary.
The left turn may now have been made in response to an emergency, not planned in advance. My larger point was that once again, what we thought we knew, what we thought was factual pieces of the jigsaw puzzle, turns out once again to apparently be false.