Is it possible to export the text and image content from topics and posts?
I would like to export the topic contents and then delete my contribution.
If I delete my profile will all posts and topic content created by this profile also be deleted?
Not that I know of. If you used/have old messages before Brave disabled messaging, you can copy past the content to an old message, then delete your post. I copy/paste posts to old messages occasionally, especially with responses that I want to reference without having to go through search or a long list of bookmarks. You can pull up your old messages by entering https://community.brave.com/u/York-Earwaker/messages in the address bar.
I think so: this is based on observation and not actual knowledge of how process works! Hopefully, if I am wrong, someone will post a correction. 
Hope this helps. Take care.