Your T will go through the appeal discussion with insurance (unless he's already had that discussion with them). Try not to panic quite yet. Generally they will go with the therapist unless you don't have a solid Axis I diagnosis.

Why did you and your T predict this would happen? Is it just routine for your insurance to automatically deny? Some are just doofuses that way. My insurance actually used to call and speak to my T every so many months, and I don't know what he said, but they never denied more sessions. (I don't think they even bother to check with him anymore after all these years. They just automatically approve.)