I made the mistake of skipping the COS-DEN leg of a SEA-DEN-COS return (we needed to continue our meeting during the drive). The GA told us we needed to pay $250 each to rebook. After a few minutes of discussion she smiled and handed us BPs and said "just get on this flight...if you like you can speak with the Gate Agent in Seattle about this and if required you can just pay the $250 fee there".
We of course somehow forgot to speak with the Seattle GA...