Middle managers exist to handle the day-to-day management of workers, so that leadership don't have to keep context-shifting between 'manage the organization' and 'manage the workers'. Today, AI is currently only able to replace workers. If, someday, AI can manage itself without direction and without costing exorbitant amounts per week to do so, then yes: middle managers will see the same work catastrophe served upon them by upper managers.

This also highlights that 'AI manager' is perhaps the most sought-after role in software engineering right now, except that workers aren't being demanding or being offered a manager's salary. Big win versus labor for corporations there, especially if they can normalize middle managers taking a career-wide pay cut while everyone is excited about AI :)