In the interest of fairness, it's important to point out that this has already been a movie, but the 1996 The Phantom, starring Billy Zane (pictured above), isn't exactly the most sincere representation of the character. Or a movie. Or a story in general. In fact, let's just say that the only superhero movie from 1996 that matters is Matilda, because Mara Wilson will always be awesome, and we desperately want her to star in a modern, gritty sequel where she magics bad guys' heads clean off.
But here's the catch that would make The Phantom work in the current superhero movie atmosphere: The Phantom dies at the hands of his villains. He's done so no fewer than 20 times, with the next kid in line always picking up where dad checked out (and handily helping the rumor that the hero is immortal). With The Phantom, the whole "hero can't die" issue would be averted. Want to do a period piece set in the 1950s? Johnny Phantom-Actor is still playing the role, but now he's the grandpa of the current Phantom and will die in the most gruesome fucking way in the final showdown.
Which would add a welcome amount of tension to situations like this.
There are 21 canon Phantoms spread over four or five centuries, which means you can kill two in every movie and still have a decade-long string of summer blockbusters, all set in different eras. Locking an actor in a long contract means jack-shit spoiler-wise, because the same actor can play multiple versions of the character. A leading actor leaving the franchise is equally simple, because is there any role on Earth easier to recast than one spread over half a millennium and various people?
Oh, Marvel might start doing this anyway to their more high-profile -- and therefore expensive -- stars pretty soon. They've got a cheap future franchise figurehead in Spider-Man now, and we've all heard the rumors that Chris Evans' Captain America might follow his comic book counterpart and go belly-up in either Civil War or one of the future Avengers films with the 20,000 superheroes in them. Shit, I'll wager that the second they gain access to movie X-Men, a new, oddly fresh-faced Wolverine will turn up with a 10-movie contract (who Cracked's John Cheese insists must be played by CM Punk), at which point all first-phase Avengers can go hang. But that won't do anything to the surprise factor; we'll still know how many movies everyone has left in their contract. No one's going to die totally unexpectedly.