Hi spikerbond welcome to the forum
I don’t know how ethical it would be to do this.
It seems to me it would be better to simply leave that forum, and start another with a fresh start.
That way there wouldn’t be any question about who “owns” the content.
Anyway, members can download a compressed CSV file of their posts with the following fields
- topic_title
- category
- sub_category
- is_pm
- post
- like_count
- reply_count
- url
- created_at
and I guess it could be possible to use that for a type of “import”
Discourse does allow for importing backups (an Admin-only feature), but I don’t think your particular use case has ever been considered.