Can't Find Logan's Scroll?
Like the comments have said, generally, in the Souls games, when an item falls off the map, or becomes inaccessible, what can salvage drops is saving and exiting the game normally back to the main menu, loading the save back up and returning to either where the enemy spawned, or close to where they fell. Most of the time, but not always, (I have had this not work) the item will just be sitting on the ground where you can retrieve it.