@palmdoc : You will not loose any discussion if you change the forum type to Category but the discussions won’t be shown anywhere as the topics don’t have any parent related. The best solution I can think of is to change the name of the forum that you would like to use as a category to something generic like ‘General’ and create a category that is a parent of ‘General’ and the other subforums you had previously.
But as I check again the link to your website, I see that you’ve found a way to organize your forums 