So the heirs of Jerry Siegel were awarded the copyright to Superman, or at least the Superman content of Action Comics #1, if you want to get technical. Pretty big score for creators' rights, I'd say, but at the same time, it's not so cut and dry. As some folks are quick to point out, Siegel and Joe Shuster created Superman before they took him to DC (then called National) and pitched him as a newspaper strip for a while before they turned him into a comic book, whereas most superheroes that came later were editorially mandated creations done as work-for-hire in the wake of Superman's popularity.
I'm of two minds on this situation. For one thing, Siegel and Shuster were definitely lowballed (even outright well and thoroughly screwed) in terms of monetary compensation for Superman, but on the other hand, the did sell the rights. And (if I'm getting my facts right) when suing for compensation later in the 40s, they did reach a settlement for nearly $100,000, which in those days was amazing money. And though they did hit hard times later on in life, an effort spearheaded by folks like Neal Adams (again, if I'm remembering correctly... please feel free to tell me if I'm not) did give them long overdue credit and some sort of pension. All small peanuts compared to what the Man of Steel pulls in through licensing dollars and such, but still.
So while I usually try and root for the underdog, well, they did sell. And for whatever reason, didn't settle for the sort of deal Bob Kane would get for Batman a year later, which somehow allowed him to claim credit for work he didn't even do. It's unfortunate, but that's the truth.
Whatever the case, I think it's a safe bet that DC - no, this goes higher than that, that TimeWarner - won't let Superman slip through their fingers completely. That S shield is basically a license to print money, after all, and they'll do what it takes to keep their fingers in that particular pie, even if it means begrudgingly cutting a deal with the Siegel (and eventually, the Shuster) heirs. So while a lot of the comics internet is speculating about the fate of Superman, I highly doubt he's going anywhere.