Remember one thing - SWA IS rich.  They are the model for all the low cost carriers worldwide.  There may be good reasons why they're not in Denver - yet.

If SWA came to DEN........ 
If UAL falls, then it is certainly a possibility...But, If UAL falls, then Concouse B is totally open. Which would mean that Continental would expand here and southwest may start service........these 2 and many more airlines....

it was announced in the Wall Street Journal today that UAL was in the process of restructuring its credit facility which would allow it to continue operating through the bankruptcy...

Basically southwest serves the places it can get gates and takeoff slots cheaply. UAL are currently in a position which leaves their fate completly up to them, sadly not all their employees see that. both pilots and more importantly management need to take a pay cut, not even a huge one, to stay afloat. If they go a hell of alot of job will go with them, it would be safe to say it could cause a crisis in the airline world. Gates would free up in Denver and more importantly O'hare. Alot of connecting passengers would contemplate LCC's more if they can get to an airport like O'hare with its high international turnover.
If your looking for an airline that may fall next, look towards USair, i cant understand why though as their service was excellent and prices competitive. That would free up a ton of gates in philly pitsburgh and charlotte all money making towns in the right hands.
Delta also posted a huge loss so they could be going, i am sure southwest wouldnt turn down a few extra gates at hartsfield. The simple fact is though. You just never know in the airline business and its almost impossible to give accurate speculation.