Reflecting further on this development, it must have Qantas absolutely shaking in its boots.
If LATAM cancels its arrangement with Qantas, it will lose arguably its second most important partnership (behind AA).
With most other partnerships/OW alliance members, Qantas has substitutes. Eg if BA left OneWorld, it would still have EK, AY, CX, JL, AF etc to codeshare with into Europe.
Without LATAM, it currently has no substitute, and finding one would be hard. Perhaps they could convince GoL for Brazil?
And it would be absolutely devastating if LATAM codeshared with VA instead because it would flip the comparative advantage between the two airlines into a massive and growing market (South America).