Why are we stressing out about this?

If you have a policy in place about after school rehearsals and grades just follow your policy and move on.

The student is taking a trip to Europe with their family, getting upset about it is not going to change their trip. They are going whether you are upset about it or not. It may seem that the family is being hypocritical but that is above our paygrade to worry about.

Teach the students who are there. When this student returns, teach them every day they are there.

Is it fair that the student is doing this, probably not. Is getting worked up or stressed about it going to fix it, probably not.

Fix what you can fix. Control what you can control. Everything else, just roll with it and make the best out of it. It is just band.