Can the midterm weight be shifted to the final exam without a good reason?

I took the MATH141 midterm today while sick and I'm estimating that I got between 70 and 80 percent which means I would need more then 90 on the final for an A. Is it common to shift the weight in cases like these? I heard it was an option during MATH140 but it was never in the sylabus. I'm going to ask during office hours but I'm impatient.