cunningham
There is a thing in Australia called the “Skilled Migrant Visa Program”. Any company that is in the position you describe would be foolish not to utilise it as this is one of the reasons why the Federal Government set it up in the first place.
The scenario you mention therefore is highly unlikely. The most likely scenario as has happened many times in the past is an upward pressure on wages as employees jump jobs in search of higher remuneration and employers offering better packages in the hope of retaining those employees they have. This results in higher inflation which triggers higher interest rates from the Reserve Bank and before you know it the economy is slowing down. Economics 101.