I doubt that corporations have the right intentions when acquiring public services. In fact, I'm inclined to believe there is a conflict of interest, and their objective may be to prevent these services from flourishing, or to sabotage them in the long term. Immediate sabotage would cause public outrage, so it's likely more subtle. This concern is evident in the recent acquisitions of GitHub and Twitter.

Seems like this would be a great job for Internet Archive, but a cursory glance doesn't show it there. I get that the *.binaries could be too much and super illegal, but maybe the text ones.

I guess one must ask El Reg to write about it. I think that might have been how it got solved a couple years ago when comp.lang.c and others were affected by this [1].

Currently, at least mozilla.support.seamonkey (not a USENET group, but from news.mozilla.org - which was shut down, but whose archived content would certainly be useful) is in that state at Google Groups. And yes, IIRC the only SPAM in recent times in that group had been posted via Google Groups...

[1] https://www.theregister.com/2021/06/01/google_usenet/