Larry Durrett knows from his experience as an owner of businesses in Fort Worth that it's not always easy to fill jobs at fast-food restaurants. But if 12 million workers -- the number of illegal immigrants estimated to be in the United States -- suddenly leave the work force, the fallout would be dramatic, Durrett said. "I hear people say we should send those people back to where they came from," said Durrett, president of Jacksonville-based Southern Multifoods and owner of about 30 Taco Bells and KFC restaurants in Fort Worth. "We can't. We'd shut down." Durrett and others --...