I’m also not sure you actually get presented that option either.. :-( When this happened to me on Qantas (only MEL-ADL so not as big a deal), they just changed my seats to economy and I only found out when my boarding pass was changed at the gate. A bit late to do much without a lot of inconvenience. You’d think they would be proactive and call or something but they don’t always.I'm fairly lucky I don't have a lot of commitments in my life, but would like to think that even if I did, if an airline ever tried to downgrade me I'd just stand my ground and ask for a hotel and a ticket the next day instead. I realise for some this isn't possible.