> I'm assuming this was sarcasm.
Unfortunately for you, I am deadly serious.
> If a [farmer|musician] stops working, there is no reason he should get paid.
There is no such thing as 'stops working'. There is a thing called 'stops providing value'.
A farmer that does not produce anything has stopped providing value to others.
A musician's the music of which is no longer desirable also has stopped producing value to others.
> it is reasonable for the creator to get a temporary monopoly.
No, he doesn't get a monopoly through copyright. A monopoly is a state where within a domain, there is only one producer. You can't say the domain of music only contains the song creator.
> After that, it's time to get working on your next creation.
You haven't presented any reason for doing so.
> What's the right time period? For a song, maybe a year. For a well-reasearched book, maybe 5 years. If you keep working on it after release, an extension might be acceptable, but even then 10 years should be the maximum. 75 years after your death? That's insane.
If your work is so good that it has mass appeal over a span of 100 years, then why not get paid for it? why do you want free stuff like this? after all, we are talking about a piece of work that would have almost unprecenteded success.