[Inziladun]

I've always thought there was a parallel between the descriptions of Sauron's permanent disembodiment and Saruman's death at the hands of Wormtongue. In both cases, the figure representing the 'divine' spirit is scattered by a wind and brought to 'nothing'. I think Saruman was reduced to an existence like Sauron's, though not for the same reason. A catastrophic loss of power caused Sauron to lose his hold on the physical world; I don't see the same causal effect on Saruman, so it's my thought he might have been 'sentenced' to a purgatory of sorts by a higher authority in punishment for such conscious abandonment of his duty and envy of Sauron as he was guilty of. Also, the seeming 'genetic experiments' he conducted with Men and Orcs are said more than once in the books to be utterly abhorrent, and I imagine Manwë (ir Eru) might have kept that in mind when considering his fate.