Thankfully the patent protection at that time expired after a modest number of years.
Thankfully patents are inforced for only 20 years. (21 possibly adding in a provisional patent application). U.S. Copyrights on the other hand have been extented to what I think is a ludicris amount of time. Life of the author plus 70 years if I recall accurately.
If I were allowed to set the rules, the length would be similar to a patent. More like 20-25 years. Then the origianal author (or current owner of the rights if sold by the original author) would have the ability to extend the copyright say... every 10 years. If the rights owner fails to reapply, the work goes to public domain. The copyright and the right to extent would of course expire along with the author if he hadn't sold the rights to some one else.
The humble opinion of one who holds a few copyrights myself.
Plaz