The Australian Permanent Resident Visa expires after 5 years, after which one needs to get a Resident Return Visa before leaving Australia, otherwise one cannot return permanently again without great difficulty.
If the Permanent Resident Visa expires while one is in Australia but one remains in Australia for 4 years then one can apply for citizenship. One does not lose one’s right to live permanently in Australia when your Permanent Resident Visa expires. You only lose the right to enter Australia.
Resident Return Visas are issued for minimum 3 months and maximum 5 years, and cost $400. They can be extremely difficult to get because the govt wants you to prove that you have a reason for returning that will benefit Australia. For example if you have a full-time permanent job (not casual) when you apply for the visa then they will grant you a visa to leave Australia and return after 2 to 5 years. Of course you lose the job the day you leave and return as a job seeker, but that is their rule. However if you need to leave to sell a house in a foreign country and return with a million dollars to buy one in Australia, they don’t consider that to be a valid reason to return because you cannot prove that you actually will bring the money. Don’t ever try to understand these rules. Just abide by them.
Australian Permanent Residency (PR) visa allows the holders to enter and live indefinitely. It is very much permanent and the visa holder can apply and obtain Australian Citizenship. However, the holder of PR visa has certain obligations like continue to be of good character, respect Australian laws.
The PR visa can be revoked by the Australian Government if the visa holder is imprisoned by the court for 12 months or more; if the visa holder is found to be engaged in terrorism and any serious crime.