just saw your post indirectly by searching for something else.
Animbom is incorrect. As your were studying in Australia, that will probably mean that you were on a student visa or something similar. Which means that your ' UK residency' is NOT affected. Its similar to people taking a gap year before going off to university and travelling on a work visa.
Im in a similar situation to you and Ive spoken to NHS Bursary team and they allow temporary absences from the UK, phone them to confirm this information. I was told that cases like ours are done on a case by case basis but the chances of us NOT getting the bursary are very small. I would still apply to the universities, then apply to get your bursary. You have nothing except a little time to lose.
Im in a similar situation to you. Im 27 and spent a year and half (one and off) working overseas because I struggled to find work here in the UK. And to me it would be ridiculous that someone could be born here, spend 25 out of their 27 years here, return to the UK and not be entitled to the bursary. When someone else not born here, could arrive at here, perhaps not work but manage to survive for 3 years and then be entitled to NHS bursary!
If your still stuck or worried speak to the National careers service. They were great. Good Luck !