Reality check? My suspicion is that NOBODY is going lose their jobs here. The word, "sack" is used metaphorically. The teachers that the outside consultant decides to replace will be placed in other Chicago schools without ever losing a paycheck. There is no ******* way the CBA would permit the wholesale termination of teachers, under any circumstances.
I worked in government long enough to know that when news reports say some bureaucrat is being "fired," it invariably means that either (a) they go on paid leave for a while, (b) they are "forced' to retire early, or (c) they are simply reassigned to another government job. In the worst cases, they will be temporarily furloughed, but will have "super-seniority" for consideration of any future openings for which they are, on paper, qualified. In effect, they get a week or two off.
What "fired" means in the public sector is quite a bit different from what "fired" means in the private sector.