It will be a big blow to cricket and Pakistani fans if the Australians do not come. It is understandable that the reason they do not want to come is because of the threat of terrorist attacks, but Sri Lanka is also no safer than Pakistan and Australians have toured them. They were also in England when the July 2005 bombings happened. It can happen anywhere.
I do agree that safety comes first, but cricket teams have never been targeted and Pakistan will provide heavy security as they have with South Africa, England, India and Zimbabwe most recently. If the Australians don't come now, how do we expect them to show up for the Champion's Trophy if they haven't toured Pakistan in more than 10 years?