Taildragger - I believe QF will be using the A330-200's for domestic initially followed by ops through to Asia when the numbers arrive.
As for the A330 going - I dont think so.
The only suitable B767 replacement is the A330 or the proposed B777 short haul variants that can do both short and medium range.
Ultimately a family of aircraft are ideal but it would have to be an amazingly attractive deal from Boeing to cause QF to back out of Airbus in the future.
Like anything else it will be ultimately politics and finance!