moderated if you want to try to export your stuff...
...just as a backup plan, truly!
This member export script worked for me. I was able to get our list of 1700 members exported to json files of 100 members each (you might be able to go bigger, I didn't try):
Note: I didn't use the chrome extension, I looked at the code and got the data exported simply by going to the URL (I think if you download the ZIP and look at it, you'll see what I mean).
Note: I did this before November.
Note: I haven't tried the companion script to download the message archive.
Hope this helps! I'm on my phone at the moment, but if there's interest, I can dig up some more info, I think I still have stuff saved on my computer.
(To be clear, we used and were beyond happy with the groups.io transfer service, I only did this download as a "just in case" backup.)