The originals were that. The originals.
Obviously you tried to keep the negatives in a safe manner because the nitrates and films were very flammable, could being eaten by fungus, decolor, or all kind of things.
Even in remastering on movies like Star Wars they went for the original negatives, which were in bad shape.
In feature films after the original negative you produced a positive then another negative as a master to produce film copies. Probably this 2 intermediate films were the best back up you could have.
Home users didn't usually back up negatives. Probably had 2 copies of the printed photos and that was it.
The original negatives had some special value, for example in investigations, historic value, etc. So people were more carefull back then.
Prior to the "inexpensive scanners" were the "expensive scanners" so you could go to a shop to use a drum scanner and have your image scanned that way.