I purchased tickets from one of the online sellers right before the shutdown. Disney extended their expiration date to 9/26/2021 but the people who were going to use them had no plans to return until December of this year. I stopped by a guest relations counter in AK when I was there in April and had them change the tickets to a new start/expiration date that matches their travel dates. No problem at all and it didn't cost me anything to make the change.