Actually, we don't know for sure what John August's script was like - but we do know that when producer Richard Zanuck described it he said that it wasn't "a soap opera," it was "scary," it was "very funny," and it carried "the Tim Burton stamp of uniqueness." And frankly that sounds very much like the way Seth Grahame-Smith's script has been being described.
And as for the rights deal Depp made, the details were never made public. It's quite possible that it's already stated in the deal that he retains the rights should he decide to do a sequel. Or it could contain an option to renew should he decide to do a sequel. Or the deal could expire with the completion and release of this film. It's all just something we'll have to wait to see...
11 days 6 hours 46 minutes 55 seconds until the day the Depp/Burton Dark Shadows is released(ET)!!