The easiest approach is to create a backup file that you can restore to another Discourse forum at a later time.
There is a discussion about archiving Discourse here: A basic Discourse archival tool. Be sure to read this post in the topic. Clicking the link in that post will show you that you can get a basic HTML version of a Discourse topic by appending ?_escaped_fragment_ to the topic’s URL. It could be possible to use that approach to scrape a site’s HTML and then save the site’s topics to a directory of HTML files.