Corn Dog Casserole

2 cups thinly sliced celery
2 tablespoons butter or margarine
1 1/2 cups sliced scallions
1 1/2 pounds hot dogs
2 eggs
1 1/2 cups milk
2 teaspoons rubbed sage
1/4 teaspoon pepper
2 (8 1/2 ounce) packages corn bread/muffin mix
16 ounces shredded sharp Cheddar cheese, divided

In a skillet saut