I'll also register for what it's worth that an escape plan probably involves an apparently unconscious and stunned Sevar being carted along with him in magic-neutralizing handcuffs or... something.
She's the only one Keltham is truly afraid of losing. His thoughts said that, over and over.
And any fake escape plan - has probability practically zero of fooling Keltham unless he wants to be fooled. Desperately wants it, needs it, to the point where he doesn't want to use dath ilani disciplines to know better. If he's already lost his Carissa - we might as well not bother, is my sense.