I have seen extra sections put in, but those tend to be more when just one city gets hit. Two years ago when MCI got snow 2 or 3 days in a row wiping out the schedule I saw something like 10 flights per day the next few days MCI/MSP.
Now with this type of thing, I'm not sure how many extra planes/crews DL has that would be able to make much of an impact. There might be but I'm not In The OCC.
I think what happens is a lot of people that were going to originate from the EC just cxld and get refunded or re schedule for a few weeks/months later. That frees up space for those who are trying to return home.
This is all just what I've noticed from experience I don't have any first hand knowledge about what's done with this type of storm that knocks out 1/3 of the country