To do that well, the post history should be reconstructed. A couple large nodes would possibly be subscribed to every mander community, so they would have a history of posts and comments which could then be reconstructed. Sadly, I think the software to do that does not exist:

https://libretechni.ca/post/1442074

As old as Lemmy is now, it’s really a shame there is no backup tool.

The mander community list and descriptions are available in lemmyverse. Unfortunately the descriptions are truncated despite someone’s request a year ago: https://lemmy.tgxn.net/post/5663028