In the future (assuming your external drive is large enough) Select the folder that holds all your photos and copy it to the external. This way you have an exact copy elsewhere, then you can easily retrieve one or more images if needed.
I personally have did this on a second internal, plus two externals. Once you loose images, especially ones you can't ever recreate like loved ones that passed away, you tend to get paranoid about not having a backup.
As for your current situation, you can try a file recover app, using the windows commands for undeleting files, or pay a service to fix it. also keep in mind that the files do not have to go to the recycle bin to be deleted. If the drive has bad sectors, etc. those files may be permanently gone. What ever you do, do not run defrag, or save any files to that drive, until it is fixed or you finally give up. As writing to the drive will write over top of any deleted files first then use the empty region. Deleting does not mean it is gone, it just means the directory was changed to allow that area to be written over. So an undelete program just changes the directory so the file is accessible again.