I've only read snippets of the book and I never got into it enough to read the whole thing.
I was never really a fan of the premise. I mean some personal anecdotes are fine but it really just came across as him telling the story of how he investigated this for the past few years. Which to me is about exciting as a school kid telling how he researched for a book report.
It's disappointing because there was great potential in a compelling Maura Murray project, be it a book, miniseries or whatever. However I feel Renner alienated a lot of good subjects (close friends, family etc) and many others are probably incredibly sick of talking about it (the Westmans, namely).
I believe many people have grown tired of the same questions and the general lack of answers over the past 13 years. The Oxygen series might be interesting given the right people are willing to talk.
Ultimately, I think this is a cold case because whatever happened to her was the result, in my opinion, of running into one lone person, leaving no evidence or witnesses to speak of. I'm completely open to being wrong on this, so while there is still focus on the case, I believe a wise move would be more thorough searches of the area. While it's not possible to entirely exclude the idea she died in the woods, the less probable it becomes the more people may think outside the box and possibly move forward towards a resolution here.