For eg, though, I read one blog post that tried explaining that once Lightroom can see the original files it would update them with the changes made to the Smart Previews. But that goes against everything I understand about Lightroom being completely catalogue based and never making adjustments to the original files!
Once the original files are available, Lightroom will render the image (not update the file) with the edits made to the smart previews. Thus the image you will see on your screen (and receive if you choose to export) the exact same image as if you had never used the smart previews, as if you had used the original full image the entire time.