Hello,
unless you checked "Move duplicates to Trash" in Preferences, there is no way to recover deleted files.
However your files are still on your computer, but on locations that you are not used to look for them. If duplicate finder finds a two pictures that are exactly the same, it will remove only one of them. Second is still at it's original location.
So if you remember names of photos/documents that you are missing, you can try to find them via Finder's search bar.
Kind regards,
Jozef Gencur