DAL was down and out a few years ago as well. Our management team under Leo Mullins did a textbook job of ruining a great brand. During BK, our management team restructured and we got some incredible people - Glen Hauenstein and Bob Cortelyou. They completely redid our network and in my opinion were the two most responsible for DAL's turnaround.
My point is that UAL could turnaround if given competent management and sword that the employees could rally behind. Under Tilton's tenure its unlikely. But a new team could definitely take advantage of what I believe is the best Hub network of any legacy and make it shine again.
Time will tell, but DAL is a vastly different beast now than we were four years ago.