I doubt that your 'bad performance' would really harm their HSC results.
On a related note, I hear that if a student is doing really badly on their internal marks and they want to drop the subject, the best time to 'drop them' is AFTER all the assessments have been done and sent in but BEFORE the HSC exams. I'm not exactly sure on why this 'works' (I'm not even sure it does) , but from what I've heard it actually boosts the marks of the other students in that course from that school.
On a related note, I hear that if a student is doing really badly on their internal marks and they want to drop the subject, the best time to 'drop them' is AFTER all the assessments have been done and sent in but BEFORE the HSC exams. I'm not exactly sure on why this 'works' (I'm not even sure it does) , but from what I've heard it actually boosts the marks of the other students in that course from that school.