Looking at the map again I can see that there is another track further north, coming from near the homestead, which we could have driven back out & around to if it wasn't getting dark. Thanks so much for opening all the gates :)
I'd be interested to know which, if either, of these options was a gazetted public road - the one we were on was on the RAA map which suggests to me that it should be a public road (in which case blocking it would presumably be illegal). The CFS map says explicitly that not all tracks shown on it are public, although the track north of the fence is named.
Google Maps still calls it Just Rd to the south of that locked gate in the direction from which we came. This may not mean anything on its own, but the pastoral boundaries map I did manage to find online had a double/parallel line along that track, implying to me that it's a gazetted roadway. And certainly my parents & I have been along it before, albeit from the north so I don't recall precisely where we rejoined the 'main' road to Tuilkilkey homestead.