Decanter One clue is that when Anak asks if he has her loyalty, she doesn't actually say yes. She says "You have always treated me with kindness, and all I have ever asked is to be able to participate in your plans for the world." This is right after Anak tells her she can't participate in his next plans. Anak may or may not pick up on this. He seems distracted.
i think he alredy take her for dead. "If your last act were to be to stop him... I would be honored to remember you that way." her action are in the end, irrilevant to him. if she can cut a couple of loose end xerces will be more free to focus on his true enemy. but in the end after he defeat his opponent he can take care of this loose end himslef. (or so he think).
Decanter That the Anak didn't already assume her loyalty is bizarre. He made her, out of a citizen of Philon who volunteered to undergo a surely risky Aka-like procedure to become part demon and his ultimate right hand. Why do that, if not loyalty? How can it still be a surprise that she'd have thrown away her life and sanity if he asked? His paranoia of her likely does not fit the man she thought he was.
yes, he was sure of her loyality under normal circumstance, but the extreme his plan involved can broke that loyality in many people, xestris loyalty was absolute, but he cannot be sure of it before they reach this very point. so he prepared his plan without take in account how absolute the loyality of xestris was. and he add the fact of simon is very skilled in earn a fanatical loyality from other, expecialy subordinate of other IKs.
another fact, we don't know when he change is plan from natural equilibrium to the absolute guardian of reality.
i think this change is recent, only when simon start collecting shards he spot the possibility of a change of pace, a defenitive solution to his struggle to keep the world balanced. xestris is a century old, i think he build her for managing philon freeing him to search a more definitive solution, but at the time he was still in his "guardian of equilibrium" mindset. so he teach xestris this.
Decanter He goes on to say "Stability, Philon, balance... these meant something to me once" - his goals have diverged from Xestris's, from the goals they may have shared once. And now, too late, she can see that. Maybe that's where his paranoia comes from - he half-expected her to figure it out sooner.
well, he betrayed her only for laying a trap to simon, without thinking a single second about her, not the danger of her task, or the risk about her, but about her a person, be treated like a disposable tool ins't great, expecialy if you think your boss should be better then this.
and yes,i think xestris will flip allegiance, soon, but not to soon. after all they need to recover zelica, and only with xestris help they can. perhaps after rescuing simon, or in the most crucial moment of the rescue plan.