Personally, I don't think every site needs a CMS. I still do simple, static sites for people who don't need many updates. Static sites still have their place, I feel.
What would happen if you deleted the html page created with wordpress that has been optimized and has backlinks connected to it.
You'd need to do an htaccess redirect to avoid errors. Preferably link to another resource, or the new location of the page.
Also I don't know for instance if the site will use drop down menus either. Would I need to redo the html/CSS completely and just convert that into say a wordpress template?
You can just add in a drop down menu to the existing theme.