As for an owner coming back for it, I have a related story.
Old girlfriend's stepdad buys a nice lifted Chevy Tahoe. A couple days later, the previous owner (who was basically a friend) came over and said "I, uh, think I left a weapon under the seat." Went in the rig and retrieved a semi-auto in a nylon holster attached to the bottom of the driver's seat. We shot the breeze for a while and it was no big deal, but had the buyer been a felon and got stopped and searched that could have been bad.
An attic gun though, I imagine fell out of a box during moving, or possibly was stashed for some reason. If it was in the attic I doubt it was very important to the previous owner.