Some airlines will cancel (without refund) the return leg of a round-trip ressie if you don't either pay the fee to reschedule, or get on *some* outbound flight within 24 hrs of your original scheduled departure (except when the delay is theirs, or an Act of God.) They are almost guaranteed to do this if you actually confess to taking a different carrier to reach your destination. Personally I consider this stealing, but they will say that "well, if you never went to destination X, how could you possibly need to return?"
I had AA tell me they would do this when I missed a flight due to a TSA problem. I debated doing a walkup outbound with SWA, but AA told me that if I walked away from the outbound flight and took another carrier to get where I was going, they intended to cancel the return without refund, which would have meant paying the walkup fare in both directions, as it was a 2-day trip. It was cheaper to pay the $300 that AA wanted to give me an alternate routing.
