Here a great lesson in the importance of keeping religion out of government. While Christians have long had sway over the school calendar, it becomes evident it won't work much longer. It seems obvious that the solution is an arbitrary calendar and floating holidays at the parent's discretion. Will chaos ensue? No more than if the status-quo continues from the looks of it. This could be the issue that keeps school doors open all year to accommodate all the possible schedule outcomes.

I think all parents should have a set number of "free days" which they can use throughout the year for whatever purpose in having their kid miss a day here and there. No "religious holiday" designation, just an across the board equal set days.

How will the teacher get any time off?

Same as they would in any other year-round school schedule. Students have excused absences all the time; using one of the days would be no different.