I don't think it is that simple. Unless the AUKUS agreement changes things the US involvement in a war with China doesn't obligate Australia. Under the alliance an attack on either country binds the other to come to their aid. An attack on Taiwan doesn't constitute an attack on the US, so Australia doesn't have an obligation to become involved. This issue came up in 2004 when the Australian government and US government had a disagreement over it as tensions rose between China and Taiwan. The US government position was that war would involve Australia if the US got involved, Australia's position was that the treaty doesn't bind us.
