I found Delta to be pretty good at waiving fees if you have reasonable documented case.

Sometime ago AC brought me late HKG-YVR and I missed DL flight YVR-SEA on a separate ticket. AC called Delta counter and they put me for free on next days flight (it was last flight of the day). I ended up buying walk up ticket on AS. After arriving to SEA, I called Delta and ended up getting refund of my nonrefundable YVR-SEA as "one time exception" (I would be perfectly OK with voucher and waved change fee though).