Re: DB's reason for publishing this book (from which the Politico article is extracted), I don't know either. However, even allowing for a degree of self-interest, I think you are absolutely right: the DNC does not survive this without a major house cleaning. We hear a lot these days about transparency: the DNC must be transparent in ferreting out the persons and the processes that left the party in ruins in 2016.
I do think the presidency of Donald Trump is going down in the flames of his corruption, incompetence and instability. In the end, the process that ends his presidency will be a political one; but the political process will be driven by the legal process: the Mueller investigation. However, from the demise of the Trump presidency, a revival of Democrats (in Congress or in the White House) does not necessarily follow. The Ds have time to pull this together; that doesn't mean they will.
"I don't belong to an organized political party," said Will Rogers. "I'm a Democrat."