I can't think of a jet that wouldn't maintain at least A100 on a single engine, therefore terrain is not much of an issue for a depressurisation in Australia.
More important, depending on the size of the aircraft, is, where will I go if the destination becomes unusable.
If I have a fire, and have to land ASAP, where will I go. Will my chosen alternate have the facilities to allow me to manage pax, exit the aircraft for a pre flight inspection, to supervise refuelling? Are there any maintenance facilities?