Gah. Typical of a book; cuts off as stuff starts to really catch your interest.
I think that they are either about to do a "back to the future" thing here, or head to the spirit world, as Kirk suggested.
I'm just glad to see Orochimaru back! ^_^ "I don't care about the war, but I still want your body, Sasuke..."
And I suppose it would be reasonable to assume that Orochimaru can manipulate senjutsu, but doesn't neccessarily enter sage mode. In essence, apparently Jugo's ability is fueled by senjutsu "chakra" or whatever and Oro knows how it ticks.