Can I reverse all settings so that my site goes back to pre-Hide My WP Ghost state?
Yes, ALL settings are reversible.
If you Deactivate the plugin first (instead of deleting via FTP), then ALL settings will revert (everything will go back to how things were) and when you delete the plugin it will be like it was never there in the first place.
Kinda like a Ghost. 🙂
Also Read: How to disable Hide My WP in case you’re stuck in front-end or if the theme is not loading properly