Nonsense ! The destruction is effective, the level, as well as the energy is zero.
Answer : the light is diffracted.
The mistake is to consider the process from the point of view of Descartes’ optics, that are no longer accurate when we reach the wavelenght scale itself. The phenomenon is explained by Huygens’ optics.
The light is reflected in all directions, but, at an ordinary scale, the waves cancel themselves in all drections but the reflexion angle, that is the only direction where there is light.
But on a CD, the spot is very small, and the light is cancelled in the direction it should reflect, but not in some other directions. Those directions depends on the wavelenght, that is the color of the light.
So the cancelled light become rainbows !
The rainbows you can see on a CD are all the light that was canceled in the direction it should have been reflected. It has not disappeared, nor has it turned into heat, it has just been diffracted.
On some phtalocyanine CDs (Ricoh, Mitsui), you can even see that the rainbows are brighter than the direct reflect of a lamp. You can also see on non engraved parts the full reflect of the lamp, very much brighter than on the groove.
If you’ve got a red (or any color) laser toy, you can also point it to a CD, and see several reflections at different angles (that are the angles where the red part of the rainbow would appear).