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Normally I'd say a 301 redirect but that's when the page has moved for good. You want domain.com to become domain.com/blog and then domain.com becomes something else. Since you're keeping the old URL I would suggest moving the page and linking to the new blog home page. Google will see domain.com/blog as a new page this way and, as long as you have new content on your main page, it's not likely to cause any issues since bots will have to spider domain.com to find domain.com/blog

Thanks for the post. Good to hear that someone else went through a similar situation! Did you do anything about any external links that might have been pointing to some of the pages that went away? Is there anything else that you could suggest that I might have not thought of? Thanks again, Scott

my client owns the industry domain name. e.g. liposuction.com. That's fantastic.  There is no better domain to have for this type of site.  I have a couple of these too. What would you do with the local city pages? I compete in local SERPs with pages that have lots of local facts, statistics, graphs, maps, links to local sources of services and information. In an effort to create authority for the domains I have authored lots of content about the most highly searched topics, obtained content contributions from experts in the field (if you own liposuction.com there might be experts in that field who would write an article for you simply because it will be published on the KW.com and visible to a lot of people.  These are not SEO articles from people who want a link they are informative content from people who have a message to spread.  Most of this content is written to be "the first document that a person interested in learning about a subject should read". Owning this type of domain gives you an enormous advantage over your competitors.