I think they'd try to avoid that. United really can't afford to buy planes right now so soon after emerging from bankruptcy. There is nothing on the market that has the performance and capacity of the 757, and United especially needs that performance at Denver.
It isn't hard to get credit coming out of bankruptcy - in fact, it isn't that hard to get credit while in bankruptcy.
Here's something from last month:
"United Airlines, the primary subsidiary of UAL Corporation (Nasdaq: UAUA), announced today that on February 2, 2007, it used cash to pay down $972 million of its original $3 billion exit facility, and refinanced the remaining $2 billion. The new facility was arranged by J.P. Morgan Securities, Inc. and Citigroup Global Markets as joint lead arrangers and Credit Suisse Securities (USA) LLC as syndication agent. The transaction results in significantly lower interest costs, less restrictive covenants, and releases approximately $2.5 billion of collateral." http://ir.united.com/phoenix.zhtml?c=83680&p=irol-newsArticle&ID=958433&highlight=