I read the book in preparation for the series, but the cool thing about the book is that there is no definitive account of how things happen. Like it will say so and so end up falling from a window. But were they pushed, did they jump, or did they fall, because there are three different accounts ongoing through the book. So HBO can go in any of those directions with many of the deaths.
They've already made a couple changes from the book that I would say so far really enhance the TV story.