Well I can answer the OP's question from personal experience.  If you have a missing item claim and AP can confirm that on the balance of probabilities it was in the burned truck then you will get a refund. You do have to wait a while until AP tries to salvage parcels that are not complete write-offs but you will get your refund eventually.

With the last truck which burnt out just before Christmas I had several hundred dollars worth of parcels on their way to QLD and Australia Post refused to pay out any compensation for them. They claimed that they could not prove they were actually on truck so I had to either replace or refund all the buyers whose parcels were destroyed.

My deepest sympathy goes to the family and friends of the driver that died in this recent fire. It is a real tragedy.

Unfortunately though, the reality is that over the next week or two, there are going to be many buyers with parcels that don't arrive. Although most will feel saddened at the loss if they have paid for something that hasn't arrived then they will expect the seller to either replace or refund.