I do believe you need some clarification here.
the RA-Aus will register anything, registration is only one of the processes of putting an aircraft into the air. Honestly, I could register a wheelbarrrow with a plank across it but that doesn't mean anything it just gives it a registration number. If you don't progress to the next step in the regisstration process your registration will automatically expire after I think 12 months.
The next step after registration is to get a certificate of airworthiness. The registration doesn't mean anything at all, it is the certificate of airworthiness which is the document that allows you to go flying. The certificate of airworthiness is available to the owner of a new aircraft after inspection by the appropriate authority, these vary from what I understand depending on the category of registration and the origins of the aircraft (e.g. kit built from an approved kit, factory built or designed yourself)
Saying that the RA-Aus deregistered your aircraft is not true, if you did not proceed with a certificate of airworthiness within the 12 months or you did not pay for the renewal of the registration then your registration simply lapses just like it would give you registered a car for 12 months and didn't renew it. Remember just like a car, it has to get inspected and signed off before it can be registered and in some states it needs to be inspected every 12 months or whatever it is based on the year of the car and the RA-Aus is exactly the same.