yahoo is going to keep the messages but just delete the art and other uploads or attachments to the messages correct? although apparently they will make some groups private as well essentially closing access.
A lot of people are going to groups.io, but I certainly wouldn't want to suggest anyone move to another centralized system. The best thing to do is probably just to get a VPS and install phpBB or something. For group owners, importing our Yahoo archives there is going to be the next task.
Yeah, a PHPBB forum on a random VPS run by a random user has a much higher chance of surviving..
The point is they then own their data. If they want to move it to archive.org or anyplace else, they can. Unlike the situation we find ourselves in now.