United Airlines will remain in its headquarters in Willis Tower for at least another 14 years. The Chicago-based airline officials say it has extended its lease in the city’s tallest skyscraper until 2033. United’s decision to stay downtown takes the airline out of play for developers looking for tenants to kick off some of the biggest mixed-use developments ever proposed in Chicago. Meanwhile, the company will revamp by adding a 30-thousand-square-foot cafeteria and roof deck on the fourth floor.