Almost three quarters of the golden age of Hollywood has been lost
This is what today's IP oligopolists would have happen to the bulk of culture.  I find it exceedingly unlikely that all IP will be maintained by the owner for the life of the author plus 70 years.  We know there are gobs of cultural artifacts from as recently as the 80s (videos, games, etc.) that are permanently lost.Without short copyright terms and the encouragement of independent archivalists, we ensure most cultural artifacts will be lost to time.