It's very simple.
First of all DO NOT PANIC
And secondly just open up your google+ account on any web browser and just go on left hand side of the browser where it says home with a drop down arrow
just choose photos from that and then u r good to go mate.
just find your photos from that collection and download them to your pc or to your google drive account.
IF IN CASE U HAVE DELETED THE FILES FROM GOOGLE PHOTOS THEN SEARCH IN THE BIN FOLDER