Yes, I was afraid that already having checked in would void any chance of refunding the ticket. A travel agent friend of mine said she thought that was the case, so I chickened out. I actually had a ticket purchased, too, which I was (of course) able to have refunded.

But isn't it possible that a businessman might be sitting at the gate with boarding pass in hand, ready to fly to JFK, and his boss calls and says he needs to go to Chicago instead. Wouldn't that businessman head straight to the counter, get a refund, then buy the next full fare ticket to ORD? You guys are the experts. Any thoughts?