There's just one problem. Every one of those pages has a different address. There's links from search engines and other sites that link deep within your site. Chances are a good portion of the traffic you have come from these existing links, and you don't want to lose that traffic. We've worked with a number of clients, optimizing their sites and building up search engine visibility just to watch it all go for not when the old site suddenly disappears and a shiny new one takes it's place.
Rankings disappear overnight.
New visitor traffic drops off. Regular visitors get a 404 page not found error and assume either the server is down or your business has gone out of business. That's the bad news. The good news is that with a little foresight and planning, these problems can be minimized. We've worked with clients to help minimize the lose of visibility that can occur during a site redesign.