On that long August afternoon a little more than two years ago, Oliver completed his notes for the book he knew he would not see. He titled it “The River of Consciousness” — the title of one of the 10 essays — and dedicated it to his longtime friend and editor at The New York Review of Books, Bob Silvers. He wrote a letter to Mr. Silvers to share this news, and within days, he received a tender letter back. (Mr. Silvers died this year.) With that, I think he felt he had done everything he could.