I can answer the original question with accuracy as a former Northern Territory Police offer, where Police in the NT are Immigration Agents and have dealt with this exact situation a number of time.

What will happen is this....
Upon attending an Immigration Official at the airport, any person overstaying their visa will be directed to a room to speak with an immigration officer in greater detail. At that moment, you are in custody, but not under arrest. You are not free to leave, and must answer a large number of questions.
You say you overstayed a working visa. . That's bad for you.
You will most likely be arrested, detained for further interviews which are not brief. Normally you will be held for several hours for interview. The outcome of the interview determines what happens next.
Regardless of which way they go, being they allow you to leave or the deport you, you will have missed your flight.
If deportation is considered or is to be done, expect to be in custody for as much 3 - 5 days.
The other option is just to hide within Australia, wait until they catch you, definitely get arrested, and definitely spend days in custody and definitely get deported.

I am reminded of one individuals case where the man did everything right, except he overstayed his visitor visa by 3 days.

The man was flying from Ayers Rock to Sydney, via Alice Springs. His flight out of Australia was per-booked from Sydney. While packing to leave, he noticed his visitor visa had expired 3 days earlier. He telephoned Immigration to advise them and ask for advice. He was advised to speak with an Immigration Officer at Alice Springs upon his arrival while waiting for the connecting flight to Sydney.
He met with an Immigration Officer at Alice Springs where he was spoken to briefly, then taken into custody and handed over to Police who held him in the Police lock-up for 2 nights. He was interviewed further. He then was put on a plane in custody to Darwin where he was held in custody for a further 3 days before being put on a flight to London from Darwin. He was deported, and refused reentry for 3 years.
He was apart from being deported, sent the bill courtesy of the Australian Government via the British Government - Darwin To London via Singapore about $3000, $175 per night for each night in detention, plus the airfare from Alice Springs to Darwin. The earlier fare he prepaid/prebooked from Alice Springs to Sydney then to London was unrefundable.

I note the original poster says he is flying out tomorrow (Wednesday). Good Luck !!

Hi Veronika,

In fact I was held in a detention center for almost 2 years and was deported from Australia more than 5 years ago ever since I have been living with my Australian wife overseas my wife has always been able to visit her family but I haven't tried to aply to get the visa do you think that I have got any hope of visiting Australia Again, before I was deported I was told that I owe th commonwealth government about $80000 I visited the Australian Consolat in 2006 and was told that I owe the commonwealth government 46000 please let me know if you have any information that might be helpful since it is getting really hard for both me and my wife to maintain this life style of hardship.

Thanks alot

Regards

We also help people who have overstayed their visas, as long as they are willing to come and talk to us and work with us to resolve their immigration status. Wherever possible, we will aim to do this while the person remains in the community.