Just a sample for those who are HK Residents, I had flown on this recently.
I was able to get CX to INVOL the ticket from North America - HKG - Vietnam to just
North America - HKG after CX cancelled the HKG - Vietnam segment.
So the agent can do it with a Non-Expired Ticket, I had not hit the 12 months validity from 1st flown segment.
2 Huge Caveats to Remember!!!
1. Once your ticket is rebooked into North America - HKG, your travel date is rather stuck without causing a huge reprice if you want to do a voluntary date change
Now you could change it back to North America - HKG - Vietnam again but I doubt that will work for those who are gone past 12 months already
2. Your reservation might get "accidentally deleted" 1 week prior to flight since the system still thinks you don't have a HKG - Vietnam segment.
But calling back within 24 hrs should be able get the reservation restored and flyable.
This is likely non-applicable to close to everyone around, but just a record on file for those in need
