It depends.
If, and that’s ‘if’ it was a qantas error, they have a contractual obligation to get you to your destination and back, and the right person in the right department should open up seats on a Qantas flight for you if JAL won’t reinstate the tickets. You’ll still fly on award seats, but Qantas will convert revenue seats to award seats to carry you.
Unfortunately our contractual rights, and sometimes consumer rights aren’t always easy to enforce in Australia. While you might have a good claim contractually, it almost certainly won’t be resolved by April if you had to take legal action.
Hopefully it won’t come to that.
If this was an event outside QF’s control, your options could be very limited.