If you leave Australia but plan on going back, you let your health insurance provider know you are leaving the country. They should be able to keep your membership 'on hold' and therefore you don't pay insurance while you are away, but you also don't lose the years you have been in and the bonus for joining before you were 30 (or is it now 35).

Just make sure that your pre-exisiting conditions will still be covered under this arrangement.