I don't think they will either, but I they'd have to offer more than 50% of all Superman related profits as is. If they want extra rights like exclusive use and all that, they have to offer more money on top of that. Besides, I kinda gleamed from the latest Splash reports that there is no deal between Siegels and DC Comics. Meaning they'll collect their 50% profits and do whatever they wish with the character.
Doesn't matter what DC will or will not agree to. They have to do it. If they don't they will be breaking the copyright ruling and Siegels can force payment through the court system.
Not 20 years that's for sure. But Siegels will see those profits. Copyright ruling makes it so.
You seem to think DC Comics is in some sort of higher power that can dictate things regardless of what the laws says. They are not. They have zero power in this case. The rulings been made, they have to follow it and pay, or go to court, lose and pay even more. One way or another they will be paying big time.
Regards, The History of Superhero Comic Books Jamie Coville
http://www.sigma.net/comichistory/