Could the rebuilding of the thumbs.db have in any way restored the associated main picture?
Not in itself, but if you consider a folder with 10 image files sat in it. If it has a corrupted thumbs.db file it could be misrepresenting what's in those 10 files, or it could even avoid showing you them (depending upon the internal operations of Windows etc). Therefore, you could be in a situation whereby you're relying upon the thumbs.db which is telling you the files are junk, and you delete the folder based upon this false information.