I have used this and it WORKS. Unfortunately they are just jpegs so no originals and the final size will depend on the preview size. However it is worth it to recover precious memories. http://regex.info/blog/lightroom-goodies/preview-extraction
Best of Luck
Yes, I've used it too, and it worked well for me. It extracts the jpeg image from the preview in Lightroom.
Jeffrey Friedl has many excellent utilities for Lightroom.