Sorry, I need to correct my last sentence to "Now, how do I get the photos to appear back in the Mac HD section of LR, with all their editing history, key word tags, star ratings, etc."
Have you tried right-clicking the name of the folder, in the left-hand Folders panel and then selecting "Find missing folder" ? or possibly "relink" when right-clicking the smart previews?
I know this is going to seem confusing to you, but the Lightroom CC forum is now for a new program that was just released a couple of weeks ago that is primarily for cloud-based use, and different program completely. The "regular" Forum has been renamed, and it would be more appropriate for you to go there to get help: