Delta Trains would simply be another arm of their business. Airline travel would not vanish but the load could be offset which means the skies would be less congested and more leg room on each airplane.
Maglev Trains tested in low pressure tunnels have been proven to achieve speeds comparable to that of todays turbojet aircraft. A massive tunnel system would need to be created under existing rail lines and the trains would operate from city center to city center cutting travel time even further.
This is manufacturing! A project this massive would create millions of jobs and at this point we can't afford not to do it. The future that would be is the Now That Is. Thanks for your time and attention.