In Comair's case the pilot contract states a certain number of airframes. That side letter of the contract is between Comair ALPA and Delta, so Delta can't just blow it off and make Comair go away.

So, when the pilot contract expires, Delta has no legal grounds to keep any aircraft on Comair's certificate.

In effect, March 2, 2011 is the day Comair's 70s, 90s, and remaining 50-seaters can be freely awarded to other carriers.

Well, not exactly free, but maybe for a dollar a month like when Delta leased the 900s to Freedom and SkyWest in 2007. Too bad Comair, ASA, and Pinnacle didn't bid a buck fifty.