Note that the disconnection BEGAN about a year ago. That means the area has had NBN for over two years. This means your copper lines could be cut tomorrow without any further notice. Basically, you are (and have) been living on borrowed time.
I take it you are currently ADSL? At this stage I would suggest one of the following:
1) Contact Optus and request they move your account to HFC NBN. It will require a copper cable be connected from the overhead wires to your home (possibly it is already in place?)
2) Contact Aussie Broadband and request they connect you to HFC NBN.
The advantage of option 2 is that it is completely separate to your existing Optus ADSL (comes down a different wire into a different box). Doing this means you can get your new NBN all set up and confirmed before deciding what to do next.
ABB do month to month contracts so you only need use them to get onto the NBN. Once on the NBN its very quick to jump to any other RSP. Just call Optus up and tell them to take over your NBN if you want. Whatever you decide make sure you contact the RSPs you are no longer using and let them know to shut your account down.