Wide eyed, people can just walk away and leave the bank holding the baby. There are precedents including Ireland, as mentioned in the article. There were similar outcomes in the USA in the past decade. The walk away scenario was not uniform in America and the effects of a bursting bubble in Australia is likely to be more damaging in certain areas like Sydney and Melbourne. Although, smaller towns in some mining areas are already experiencing significant drops in house values.
The thing most politicians don't understand is that households can't ride out unemployment/downturns whilst carrying high levels of debt. If they did comprehend this detail the Treasurer (in the last fortnight) wouldn't be talking about the ability of the private sector to drive the economy right now as a result of low interest rates. This is beyond irresponsible.
When will the bubble burst? No one knows, but the potential for a very nasty situation is very real. The degree of the problem could have been minimised if governments of all persuasions had not abandoned reasonable financial and banking regulations.
If the unemployment/underemployment rate continues to rise, asset price decreases are almost certain. No job, no house, no assets multiplied by one million or more people will be a disaster. If governments of the past twenty years have looked clueless when things have been going quite well, imagine what the current government will look like if the millions of debt laden households go beyond the tipping point.