If I agree that you may miss the midterm, there will be no make-up midterm. Instead, the weight of the final exam will be increased to include the weight of the midterm. For example, if the midterm was worth 20% and the final 35%, the final will now be worth 55%. But this is NOT a free choice.
If you inform me afterward that you were unable to write the midterm, you will get a mark of zero.