WD My Passport has deleted an entire directory

I had to send my MacBook Pro away to be repaired. So I backed it up completely onto a 1TB WD My Passport. Then I plugged the WD My Passport into my MacBook Air to access some of the files that were on the MacBook Pro that I sent away for repairs. Today, I have discovered (to my consternation) that the entire backup of my MacBook Pro is gone! I’m guessing that WD Passport has overwritten it? Would this be correct? Is there anything I can do to restore the backup from my MacBook Pro?