Lightroom contains low resolution thumbnails of your photos. They are unlikely to be useful in printing. Nevertheless, you can try to recover them using this plug-in: Jeffrey Friedl's Blog » Jeffrey’s “Extract Cached Image Previews” Lightroom Plugin
Only if you had built smart previews for those images.
Else go to the location where you have your catalog, look for a folder names Lightroom Catalog Smart Previews.lrdata
Open this folder and you will see a lot of subfolders, these subfolders have dng files, which can be easily converted to jpeg.