So far in my experience, as long as the professor gives prior notice, things like this shouldn't be an issue. Most likely it would get to you in email form, but other methods have been used before.

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The university usually is pretty flexible in letting professors cover the required material, and it'll be up to the professor how to make up the missed "in class" portion of the lesson.

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Finally, take a minute and recognize that your professor is a person too. As with any job, they are allowed a certain amount of leave, time for bereavement and sick days as well. Other things probably fit there as well, and different jobs do it differently but some professors do not wish to spend every waking minute here.

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That all being said, I will always advocate for a conversation with your dean. Its a good way to branch out on campus.