Upvote:2
You should be OK. As an Australian citizen, you have an unconditional right to enter Australia, and your travel document (passport) will still be valid when you show it to the airline at check-in.
Schengen exit immigration in DΓΌsseldorf will not stop you from leaving, and you will not go through immigration at all in Hong Kong. (Note: I'm assuming your flights are booked on the same ticket, which I hope is the case if you only have an hour to transfer.)