I think he's as free to be as unconventional as he needs to be to give us a chance of winning, if our goal is to win, which I think it is.
If (as Fatprop suggests) we have a 10% chance of winning by playing conservatively (and that's generous, if you calculate the knockout odds realistically) but playing unconventionally increases that to 20%, while also increasing our odds of crashing out in the pool stage to 60%, do we take it?
Yes we do! Of course we do. It's the world cup. Death or glory. We should aim to win it.
There'll be carnage on the Internet if we crash out in the pool stage by taking risks against England and Wales, but so be it. No one is going to accept, with hindsight, that the risk was acceptable, if it fails. That's not how hindsight works.
But: there'll also be carnage on the Internet if we finish second. Probably the same carnage. There'll be an angry thread on here demanding his replacement. The Roar will explode. Cheika's only chance of public acceptance is to win.
And that's game theory.