I may be ignorant about the airplane graveyards, but it seems to me if they are good enough to fly to them, they are good enough to fly out of them -- initially.
I've seen a lot of photos of 747-100s and 200s just sitting there and deteriorating. After a while the engines disappear. Then the electronics, etc. But what is preventing an upstart cargo airline to buy these still functioning aircraft (before piracy) at a real cut-rate price?
I agree that there is not much call for the Convairs, but the 747 series is by no means dead to the world, especially when it comes to cargo.