If Australia want to do this, I really hope Haddin and Johnson get promoted earlyish. Reason? You'd only abort after you are 4,5 or 6 wickets down and the prospect of Haddin and Johnson trying to defend for a draw is not one I'd be relying on. Get them up the order - use their attacking ability while the game is winnable and try to get the Windies on the back foot. If it doesn't pay off, then you have much better defenders like Hussey and North to ride out for a draw.