Though I'm not a user and never liked the service myself, I'd like it to be preserved. It is part of internet history. Let's not let happen to answers what happened to geocities.
https://slate.com/technology/2019/12/yahoo-groups-is-ending-...
But your point stands, looked at as a whole, and with data mining, I guess they could gather something about common words uses, time spent on the internet etc...
But I wonder who would really care about the flame wars, and chit chat 200 years from now.
[0] https://www.forbes.com/sites/kristinakillgrove/2018/05/11/me...