It is very doubtful there is any need to search posts. The data are still necessary for the purpose they were originally collected, and there is also a archiving exception which may apply.

If I was them I would just send the person their login profile and delete that from the site. Everything else is excepted, including backups which are kept for security.

A good community example to look at is Wikipedia. I will star to worry if and when I see them start deleting profiles and articles. Until then I see this kind of articles like a bit of scared interpretation of how nations might implement and apply GDPR.