I don't have detailed knowledge of opps, but my best guess is not really. Don't forget, there isn't really just "skipping a day," since the same aircraft may fly various different routes everyday. It's not like the same plane routes between the same two or three cities all the time. A plane may criscross the US one direction one day through a few cities/hubs, then cross back on different routes the next, not necessarily going back to where it started.

I suspect they do try to get more flights out of ORD ahead of time, so they can move around the planes to fly to other destinations not affected by the storm. These planes, I suspect, can be subbed in to run flights that were scheduled to be run by aircraft now stuck in ORD.

Then again, maybe I'm completely wrong. But one thing's for sure - I wouldn't want to be one of the UA guy's doing route/fleet planning for the next few days.