Butter a 2-quart shallow baking dish; arrange bread slices in dish, overlapping slightly. Place sausage slices between bread slices.
In a large bowl, whisk together eggs, milk, maple syrup, and 1 teaspoon salt until combined. Pour egg mixture over bread and sausage, pressing down on bread to submerge. Cover dish tightly with plastic wrap; refrigerate at least 2 hours (or up to overnight).
Preheat oven to 350 degrees. Remove plastic wrap, and place baking dish on a rimmed baking sheet. Bake until strata is puffed and set in center, about 1 1/2 hours (tent with aluminum foil if browning too quickly). Let cool 10 minutes.
While strata cools, whisk together oil, preserves, and vinegar in a large bowl; season with salt and pepper. Add lettuce and grapes; toss to combine. Serve strata with salad and, if desired, additional syrup on the side.
Overlapping the bread slices gives the strata a nice golden-brown crust, even as it soaks up plenty of the egg mixture.