On the other hand, Joe Plumber can just as easily die young and leave a destitute family. Does that mean that we have to make a law that all clients of plumbers have to make annual payments to their plumbers and their descendants for up to 70 years after the plumber’s death?

When a plumber does a job, they get paid for it in full immediately. When an author writes a book, the income comes in a trickle over an extended (but in theory fixed) time period.

If a plumber and an author were to die young, the Plumber's family have already benefited in full from the results of work the plumber did before death, because payment in full was made immediately when the work was done. What you are arguing for is that the author's family should not benefit in full from the work the author did in life. Why is that?

Only if the clients were going to make those annual payments anyway.

Consider the scenario in which a plumber does a job, then dies before he gets paid. Should that invalidate your debt, or should you still pay what you owe to the plumber's estate? It seems obvious that it's the second one.