The coverage of this incident that I read several months ago (if it was the same incident) said that when it was announced that the flight was cancelled, the four Arabs at first refused to leave and demanded that the plane take off. After a vehement argument where the Arabs argued the importance of their "mission" (my word) with I think the pilot and flight attendents, they seemed to have a sudden change of heart and literally ran off the plane and disappeared into the airport crowd.
But the more I think about it, I seem to remember that that report was about another flight from Boston's Logan - where 3 of the 4 hijacked planes originated. This Dallas report may be a totally seperate incident.
Anyone out there remember??