Your photos have not been deleted. They have just moved to a new location. The new Photo App has replaced your camera roll and PhotoStream.  Your photos that had been in PhotoStream are now in Recently Added.  Recently Added consists of photos added within the last 30 days on you iOS devices.  If you delete a photo here it will delete off of all of your devices. In order to view your older photos, you need to use the Years, Collections, and Moments views.