I’ve been running into a lot of people who are using their blog as their CMS lately, and who want to combine them with MailChimp. I usually recommend they create content in their blog, then publish it to their email list automatically via our RSS-to-email tool. Believe it or not though, there are people with valid business cases for going in the opposite direction: from MailChimp to blog. All we could do for them in the past was recommend they change their business model (not exactly an ideal pitch to customers).
Thankfully, Mark Parolisi has created a WordPress plugin for MailChimp that "fetches your campaign archives and either creates them as posts in your WP database, or just displays them live by fetching them from MailChimp upon request."
Give it a shot and let Mark know if you find it useful. Oh, and some other WP plugins for MailChimp you might like: