I may very well come back. You being "down under" I don't know how much more growing seaqson you have left. I have had tomato plants reduced to a stub from hail and have come back and done just fine.
If your plant is really stressed now what have you got to lose. May be if after you cut it back you could rig up something for shade for it until your weather is a little cooler. Live and learn is a good motto for gardening.
I just remembered maybe your heat stress problem is wind related. If you could give some protection from the hot drying wind it should help.
Out here in eastern Colorado its usually too cool at night and too hot during the day. We planted a Black Krim next to the house so it was protected from the north and west. Eventhough it got a lot of heat-mostly reflected from windows and the steel siding on the house- it grew into a monster that had to be pruned just to get to the fruits. Hope this helps.
They might come back. We have that problem here in the desert in Arizona, the August heat kills them off pretty badly, but they make a recovery in late September and put on a second crop of tomatoes.
It may depend if it is a determinant or indeterminat type tomato. If it is an inderternimant, I would say it will take off again. If not, I'm not sure.