Here is a different plug in that does a reasonable job:
https://wordpress.org/extend/plugins/bbpress-post-topics/
After installing it, go to discussion settings and then set it to create a forum topic for each post, copy tags, etc. Then you have an option to apply settings to all existing posts.
I tried this on a test site and it worked pretty well. It did not do all the bookkeeping of reply counts correctly, but it did create appropriate topics for each post and import the comments and replies to them. Local bookkeeping services
It is also reversible as it does not delete either the posts or comments — if you deactivate the plug in your posts (which were unchanged anyway) and their comments are intact. You do still have a bunch of new topics in your target forum.
yes, I also removed the add-in
