Diagon

Verizon's response, and the response to the response, are in the article of the OP. They claim they offer a Group Downloads Manager, but it's very broken.

But the data will be going to Archive.org, correct?

Yes. The archiving was starting to take a lot of bandwidth. Some care had to be taken not to bog down Yahoo's servers.

They do it regularly. Lead in gasoline (ethyl corp), asbestos.

See below. My main concern is early medical/biohacking groups that shared data, like medical tests, and engaged in extensive discussion/community driven research. Such groups go back to at least the late 1990's.

A main concern of the Archive Group (again, below) is art that was uploaded there.

I'm sure those are not the only two classes of examples. See for example the bird watching group in Delhi that has been collecting data for decades. (In the link of the OP.)

Individuals have always been able to delete their own posts. If you log in there, you can still do it (before the 14th).

Also, see betamaxthetape, above. If anything is archived, they will respond to takedown requests.

Is this something you know from the inside, or your (probably good) guess?

It's not stupid. There were serious groups using that platform. While I never thought it was a good idea, they nevertheless did. My personal concern is community driven medical/biohacking research groups that go back to at least the late 1990's.

They hadn't backed up yet. They had set up accounts with yahoo that they were then planning to use to back up those groups. Backups themselves were starting, but they had to go slowly enough not to bog down yahoo's servers.

While the above post is concerned with Fandom groups, my concern is with groups that started doing early community driven biohacking type research. There are medical tests results and discussions of medical interventions. While that's my focus, I'm sure there's additiona important material. We really need to save this data.

There's way too much data. Many group owners did not know of the shutdown (Yahoo was negligent regarding informing owners), and even if they did many group owners have little or no technical capability. That's why so many requested of the Archive Team that their groups be archived.

Many groups are public. Many have owners that requested the group be archived.

While I agree with your first point, and tried to get groups I was associated with to move for years, nevertheless there are groups there that engaged in community driven research and have important data uploaded there. (This is my main concern, though other groups were focused on different issues - uploaded art, for example.) So I think while we need to educate people about not using centralized providers like Yahoo and Google, right now we need to focus on getting someone at Verizon/Yahoo to respond to this urgent situation.

Extensive history is about to be lost. Despite being broken, many organizations still use it. Examples from that post:

A police cooperative in Washington DC that was using them as a network to communicate with their respective neighborhoods with over 17,000 members.

A phone company in the UK that assigns phone numbers using the groups and now will lose all those phone designations when it’s deleted.

A Birding group in new Delhi with 2,000 members that has collected data and research on birds for TWO DECADES.

An Adoption group in France, that has been using it for years and years to communicate and share history and photos and more.

They also would have found: Numerous support groups for people who are suicidal or depressed.

Numerous medical groups for people to communicate more effectively with their doctors.

Numerous Vet groups with 24 hr care advice for sick pets.

Numerous support and help groups for the Elderly.

Numerous Historical groups for WW2 Veterans, Vietnam Veterans, and etc.

Numerous science groups that have used them for years and have all their research there.

Numerous fan fiction groups or arts groups that have shared their work for years.