It is not possible to derive exact information from a decayed state
That's true in the most general situation, when there is no prior information available. But a brain is not a random chunk of matter, it's a highly particular one, with certain patterns and regularities. So it's not implausible that a superintelligence could restore even a moderately damaged brain.
For a real example, think of image restoration of natural scenes. A photograph is not a random matrix of pixels, it belongs to a very small subset of all possible images, and that knowledge allows seemingly "impossible" tasks of focusing, enhacement and all that.
So it's not implausible that a superintelligence could restore even a moderately damaged brain.
Intelligence is not magic. Information that no longer exists cannot be reinvented with fidelity.
For a real example, think of image restoration of natural scenes. A photograph is not a random matrix of pixels, it belongs to a very small subset of all possible images, and that knowledge allows seemingly "impossible" tasks of focusing, enhacement and all that.
And yet still-shots are limited to their original resolution; anything further is artistic ...
I know celebrities cryocrastinate just as much as anyone else, but King seems like the kind of guy to go through with it.
http://www.cnn.com/2011/12/02/showbiz/larry-king-i-want-to-be-frozen/index.html?hpt=hp_t3