There's some good thinking on this thread.
But to be the Devils Advocate for a moment: let's look at the the consequences of his leaving our game and not being available for the Wallabies.
Let's face it: the Wallabies despite being in the top 4 usually, is not a lot different from other teams, except the All Blacks, who have strengths in most areas, especially in the top two inches, and not a lot of weaknesses.
The Boks are tougher physically but that didn't show recently; France had an often brilliant 6N all across the park, but we know how hot and cold they are - and they were cold in the RSA and Argentina recently. England have the best structure in their game, which is both good and bad.
Wales has similar strengths and weaknesses to us; and Ireland, without ROG, is so close to us in type that it doesn't matter.
What we have that is different from all these teams is the Genia/Cooper nexus. No one else has that. We haven't seen them against the All Blacks yet and they weren't that influential against England in Sydney, but it's the kind of combination that can win games that may otherwise be lost. It isn't that bad either if they are average since in that case they are scarcely worse than any other 9/10 we can come up with.
Let's try to keep Cooper by going a little further than may be proper.