After you already did many sectors on the RTW changing to something else should cost you lots of money.
So it looks like you have two options:
- Buy a seperate ticket from your current location to get home and back to Australia. Australia is actually a fairly good place for inexpensive tickets in premium classes (or use miles) and then restart your RTW later - als long as the last flight is not more than one year after the first you are ok
- Or if you just want to get home and don't want to continue skip all the short segments, reroute to someting like SYD-JNB-LHR-xxx