Looks like they might restrict the lead to around 300.
Just imagine how strange it would be if Clarkey & Co. actually came out to bat with the intention of batting for a couple of days and putting on 500 to stand perhaps some chance of staying in the game, I can't imagine it, I don't think they're capable of even trying. It's like when India are under the cosh, it's a waste of time watching them bat. I'll keep half an eye on it in case something incredible happens with the ball again for england but essentially, there's no point waiting to find out what Australia will do, they'll play unecessary hoiks and cuts, chuck their wickets and get it over and done with.
Modify: It's also what England did last ashes down under, to be fair.