I'm not surprised at all by Maggie's behavior - she was Parson's right-hand unit through most of TBFGK, relaying messages, giving him energy boosts when he was tired, and just generally being an advisory-type person. She's also expressed gratitude to him, and, even more importantly, profound respect - she has stated she believes his mind is their most formidable weapon, and calls him a great warrior in one of the last pages. Maggie also seems, moreso than even Sizemore or Wanda, to recognize Parson's real genius. This combined with the fact that he's just won a crazy battle probably has her loyalties shifted towards Parson in terms of just his raw leadership ability. However, I think there's also something to be said for the fact that Maggie is aware of Parson's consciousness of the morality of his actions (given their talk at the end of the book about her being only the third biggest monster on the mountain), and credits him with what Ansom would call "the moral fitness to lead."
I think this update just really shows how Stanley is falling back into his old tendancy to "promote the pretty-boy," only this time the pretty-boy actually has leadershp potential. For all his 'growth,' Stanley still gets caught up in the the idea that aesthetics = goodness/prowess. Come to think of it, that's probably why he underappreciates Sizemore and favours Wanda; Sizemore resembles a middle-aged bald man who specializes in and works with crap, while Wanda has the form of a young, attractive woman. The fact that Sizemore's an honest, loveable, sweetheart of a guy, and Wanda's a power-hungry, manipulative woman are completely lost on Stanley since all he looks at is the overt aesthetic quality of other people. That's why I think he's so apt to demote Parson in favour of Ansom - in spite of Parson's incredible skill and cunning, he's not as aethetically pleasing to Stanley's eye.
The single most hopeful thought I can imagine resulting from Parson's demotion is that he and Sizemore will become good friends again. Sizemore seems to already be working hard at trying to be friendly, but I really, really would like them to be true friends again. If Parson does end up defecting, I'd like to think that Sizemore would join him, maybe even Maggie. That would probably be Stanley's downfall - his shortsightedness with regards to these three coming back to bite him in the ass. I think he sees Wanda as his aethetic equal, and is definitely now forced to see her as his fated equal as well, but when it comes to Parson, Maggie, and Sizemore he still daftly underestimates them.
The swear at the end is brilliant! I can't wait to see how Parson's going to break the game...
Edit: Additionally, I'd just like to say that anytime some says something along the lines of "the Titan's have a path for us, but it's not always clear," it always makes me smile to myself - they're such delicious metafictional moments in that the characters themselves are an inch away from realizing that they are actually characters in a story being told by Rob and Jamie - our Titans