Is the plan to put the site in “cold public storage” for a time and perhaps re-start the forum later? If that’s the case, then just saving the backup (rather than wanting to re-import the data back to Discourse later) solves that problem and would allow people to be re-connected with their accounts.
Or, do you want to periodically push off part of the live forum to another static site?
You want just the topics and not user pages? Are internal links important? Is a single text file per topic what you’re looking for, or would you prefer HTML that preserved at least some formatting and images and such?