Mix chicken, hot sauce, and ranch dressing together in a bowl until coated; set aside for flavors to blend.
Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until cooked through but firm to the bite, 8 minutes. Drain and transfer back to the pot. Stir margarine, milk, and cheese powder into pasta until sauce is smooth.
Pour half of the macaroni and cheese into an 8-inch square casserole dish; top with chicken mixture, celery, and blue cheese. Spread remaining macaroni and cheese on top of blue cheese layer.
Bake in the preheated oven until chicken is warmed and casserole is bubbling, about 15 minutes.