Two optional automations in Configuration > Theme: Kitchen deal with that:

• Select Previous Menu if Meals are not selected for Delivery Date on Cutoff Day – on the cut-off weekday, for each open date in that weekday's window that has no Meal Prep menu for a kitchen, Sprwt copies the most recent earlier menu (searching back up to 30 days) onto the date so customers can still order.
• Send Email If Meals are not selected for Delivery Date on Cutoff Day – emails you a warning listing the dates that are missing a menu.

Both default to No. Without them, such dates simply appear as No Menu (grey) on the dashboard calendar and customers cannot order for them.