Have they fixed the interconnector from Victoria to Tasmania, yet?
Yes. Basslink was finally repaired and made operational a few months ago. Although with the amount of rain they've had, they are probably self supporting on hydro at the moment.
So it is one big grid that cannot be isolated into "sections"
If the interconnector can isolate SA as a state from the national grid, surely one can isolate sections within a state.
Depends on how the infrastructure is designed. Also, it isn't isolated by people - it's done by automatics. When large isolations occur, sudden changes in demand can cause upline ripples. These become bigger and bigger as more load is shed, causing things like the heavily protected interconnector to self isolate.
Eyre peninsula, now powered, is still only just hanging on via one transmission line. They had a blackout for over two days because all three transmission systems were wiped out. They had to repair one temporarily, isolate the other two, and then slowly bring it online.
The transmissions towers are made to withstand a 1 in 100 year event. This means FNQ infrastructure is much stronger, to withstand cyclone force winds. Do people expect every building and structure in the south if the country should be built to cyclone standards? That would be unnecessarily expensive.