If you are absent from school, you have to write a sick-note. → This sentence is correct as it is.

Unless you write a sick-note, you cannot return to school.

If my sister didn’t have a terrible headache, she wouldn’t be absent from her class. → This sentence is correct as it is.

Unless she had a terrible headache, she would not be absent from her class.

Unless he refused everything, he would lose his family. → This sentence is correct as it is.

Unless I saved my money, someone would take it. → This sentence is incorrect. The correct sentence should be:
If I didn’t save my money, someone would take it.

Unless you had stayed at home yesterday, you wouldn’t have enjoyed a delicious meal. → This sentence is correct as it is.

If you had stayed at home yesterday, you would have enjoyed a delicious meal.

Unless he had been busy last night, he could have met his friends. → This sentence is correct as it is.

If he hadn’t been busy last night, he could have met his friends.

If she hadn’t missed the bus, she wouldn’t have been late. → This sentence is correct as it is.

Unless she had missed the bus, she wouldn’t have been late.

Unless you lived in the dormitory, you could annoy me. → This sentence is incorrect. The correct sentence should be:
If you didn’t live in the dormitory, you could annoy me.

Unless the student goes to school early, he will be punished. → This sentence is correct as it is.