As I said upthread, if Pos knew (or assumed) that Paterno knew of the 1998 investigation of Sandusky, then I don't think the other facts in the Freeh report are all that important to his book.
Of course, that one fact changes how a lot of other, previously known facts are understood. For instance, Paterno's explanations cannot be taken at face value, because he lied repeatedly about this point. (Even if you think his age is a mitigating factor, that still cuts against trusting any of his other recollections.) Also, I have to think any tortured rationale one might construct to defend Paterno's inaction in 2001 is blown to bits by the fact that Paterno knew that police had investigated a previous, similar incident.
So, if Pos was writing his book on the assumption that Paterno lied to him when he said he didn't know about the 1998 investigation, then all he has to do is revise a few sentences to reflect that his assumption is now historical fact. (A lot of other details have to be fact-checked too, but I assume he has editors for that.) On the other hand, if Pos wrote his book believing that Paterno's lie was true, or at least plausible, then he will have to rewrite parts of the book completely, and may even have to reconsider the entire tone of the book -- which is too large a task to complete between now and the publication date.
With no suggestion that the Freeh report will delay the publication of Pos's work, there's little to do except hope that his book strikes the right tone.