Valid point and it's a tricky argument. Obviously it is nice to be able to take care of your family in the event of a tragic situation occurring.
How about the estate gets the copyright for the duration of the original copyright? Lets use the 14 year copyright the GP mentioned.. if the artist dies ant there are still 9 years left on the copyright then the estate could retain the copyright for 9 years. If there is only 5 months left then the estate only gets the remaining 5 months.
This way, the copyright is honored to it's entirety and the estate benefits, assuming the copyright hasn't expired already. True, it would suck if the copyright only had a month left on it and the holder died and didn't leave much for his/her estate but that could be chalked up to bad planning (for emergencies) as the copyright has already payed out as much as it was ever going to.
Much of anything more, I'm afraid, could be easily abused (as it has been already). We could use the argument that there should be an extension so the family can continue being supported... but then what if a corporation gets the copyright.. just think of all the people working at the corporation and their families....
Copyright should not be a retirement plan.. not for the artist and not for their estates or corporations.