Interestingly, I search everywhere online, couldnt find an answer to this, or I have looked at wrong places. Anyway, I hope someone can help me out with this here...

I'm closing down a site, for visitors who arrive at my site, I would like to redirect them to a closing down notice page. But under the root, I have a sub-directory, which holds the files of my other domain, and I would like to keep it as it is. I guess I can use htaccess to fix this, but question is: how?

In summary:
If its under the root -> redirect
If its under the sub-directory -> do nothing

Remove all the files and add a custom 404 page.