Over my head. You're gonna hafta be more specific. I ain't that smart. Only if you feel like it, though. :)
Some of the things it assumes without proving in more detail:
1) That the soul only means the combination of a body and breath of life (which is in itself undefined, and the manner of it's return to God is undefined).
2) And assuming this is even true, for their definition can be assumed, it does not prove that the dead know nothing, say if one holds the soul and spirit are separate, or soul and mind, that knowledge can not come to it. Ecclesiastes 9:5 is used of this verse but there is no reason to think that this means the dead know absolutely nothing for then it would not be the case that Samuel, or Moses, or as a certain person thinks also, Elijah, could speak, which is associated with knowledge, and the same word of "spirit" or "breath" is used of Samuel. If it is then said "they can not know without being in the Earth" then the passage means that they can not know the things of the living, which is used by the author of this article of the very next verse.
3) The above last sentence if true does not prove an absolute state of the dead, if it does then this assumption must be proven too.
4) "Sleep" is said to be unconsciousness, this is an assumption and is not defined. Moreover what exactly is meant by the dead sleeping is not defined. An alternative solution (no less valid) is that it refers to the position of the bodies in the grave, this is also an assumption yes, but why should I assume it means unconsciousness? Define it from the Scriptures and prove it.
5) "Soul" itself needs proof that it only is the breath of life and the body, for if the disunity of that is meant by "ceases to exist" then sure, the soul (in that sense, which is still not defined) ceases to exist, but this does not argue against what the "immortality of the soul" means.