Did Nathaniel actually die in the bartimaeus trilogy?

It is uncertain whether or not he did die, and in fact his absence suggests that he might have. However, it is mentioned in one of the earlier books, Amulet of Samarkand I think, that sometimes a spirit who has been imprisoned for a long period will grant a favor or favors to the individual that freed him. Under this rule, there is a possibility that the two that were in the staff may have protected or spared Nathaniel in gratitude. But then again, they could've been some of the more ill-spirited types and could've killed him. Up to the reader to decide I suppose.