In the very latest edition of The Wrestling Observer newsletter, Dave Meltzer reports that the idea of Sting signing with WWE is no longer considered a sure thing. This contradicts just about every other report that has been released regarding Sting's contract status, as it's been widely assumed that it wasn't a matter of "if" he signed, but rather "when".
This isn't the first time though that Sting has been very close to a WWE deal and then decided against it. He's referred to this fact in several interviews in the past.
The majority feel that Sting will sign still at some point, but it seems like there's a small sense of doubt starting to leak into the picture.