OP

1. By not speaking with CX, you leave yourself open to CX saying that they would, of course, have accommodated you by rebooking onto Qantas and therefore that they need not refund you anything. As to the new ticket you purchased, that is your decision and has nothing to do with CX.

2. Nonetheless, I would visit a CX ticket office at a non-busy time. Bring your e-ticket receipt and explain in cool, calm and collected terms exactly what happened. It is possible that you can at least obtain a credit for future use for the value of your unflown segment (which will not likely be 1/2 of the ticket price).

3. It is far from "lecturing" for others to raise the travel insurance issue. First, OP may have travel insurance and be focused in the wrong place. Second, others gain valuable insight when problems repeat themselves. If OP does not have travel insurance, having had two recent tough experiences, perhaps he will obtain it. Others in OP's situation may choose to purchase it. Indeed this would have been easy if OP had travel insurance. Presuming relatively common terms (always worth reading carefully), he would have been reimbursed for his Qantas ticket and the insurance carrier would deal with CX.