Having said that, we are actually leery of ANY copyright that extends much past the death of an author.
The truth is that copyright has contributed to more modern great artists being FORGOTTEN than anything else. Great writers can't be remembered when their works immediately go out of print as soon as they die unless their heirs are capable of managing their copyrights, which many heirs aren't.
If we want our work to last 'forever', the best thing to do is set it free.