Each page on website can either have content of it's own or be a redirect to another url (e.g. blog):
- In case if page have content, then it can be accessed via http://www.website.tld/path/to/the/page.html
- In case page has external url specified, then all links to the page on website would actually be to that external url.
It turns out however, then if visitor manually types in url to the page that it had prior to becoming external page, then it's possible to see former content without issues.
Do a regular 302 redirect in case if accessed page url is configured as external page.