As noted in Yahoo’s tweets, you still won’t be able to view content on Yahoo Groups after December 14th. Yahoo stopped allowing users to upload content on October 28th, so Yahoo Groups have already become pretty limited.
Once Yahoo deletes the data, a significant chunk of internet history will be gone for good. Some archivists say they have been joining groups using “semi-automated scripts” in an attempt to archive data before everything is deleted, but Verizon Media (which owns Yahoo) has apparently banned 128 archivists, saying that their actions violated its terms of service, severely hampering their archival efforts.
A Yahoo spokesperson said that the company has also extended the deadline for when it will convert public groups into restricted groups to January 31st. That means if you want to join a group after that date, you’ll have to request an invite or be invited by a group admin.