The assumption that the announcement was not previously agreed with Qantas is clearly not correct.
The best thing that could possibly happen to BA would be that Qantas abandoned the partnership arrangement between Austraila and the UK and Europe which is very much to Qantas advantage, while inhibiting BA from maximising its own business and interests in Australia and much of Asia. It is therefore very unlikely that Qantas will abandon the arrangement which is so much in its favour.
Only the core route from Sydney and Melbourne via South East Asia to London is fundamentally profitable. All the rest is at best marginal/unprofitable and these are the routes Qantas flies,- so who pays??