Cook sausage in a large skillet over medium-high heat for 8-10 minutes, stirring often, until it's thoroughly cooked; then drain any excess grease. Allow it to cool slightly.
Open the can of cinnamon rolls and place the icing in the refrigerator.
Separate the dough into 8 rolls and cut each one into 4 pieces. Arrange them in the bottom of a 10x6-inch baking dish.
Evenly distribute the cooled, browned breakfast sausage over the cinnamon roll mixture.
In a large bowl, use a whisk to beat together the eggs, milk, vanilla, and maple syrup until they are well combined.
Pour the egg mixture on top of the cinnamon rolls and sausage.
Bake the casserole, covered, for 30 minutes. Uncover and continue baking for an additional 15 minutes, or until a knife inserted into the center comes out clean and the cinnamon rolls on top are golden brown.
Before serving, gently reheat the reserved frosting in the microwave for a few seconds until it's just pourable. Drizzle the warmed frosting evenly over the top of the baked casserole.
Notes
Prep Ahead Tips: Cover and refrigerate overnight. The next morning, let the casserole sit at room temperature for 30 minutes before baking.