Will deleting a highlight in Readwise delete the original or vice versa?
If you delete (or discard) a highlight in Readwise, the highlight in the original source will not be deleted. This includes Amazon Kindle, Apple Books, Instapaper, Pocket, and other integrations. Similarly, if you delete the highlight in the original source, the highlight will not be deleted in Readwise.
The one exception here is if you delete a highlight from Amazon Kindle and then force a full refresh. In that case, any previously imported but now deleted highlights in Kindle will also be deleted from your Readwise account.