The CEO has talked about a replacement not arriving till after 2020, so it is a few years off yet, the youngest 330 is less than 12 months old and the oldest 3 or so years old, so they have plenty of life in them yet.
I would think that when the time comes the 350 would have to be in the hunt given that Qantas and jetstar have gone/are going the 787 route. It is hard making yourself look different if you have the same aeroplanes. Much easier to point out the differences between you and your competitor if you have a different airframe, particularly given the 350 is newer in the marketplace and has a range of airframes that will meet the range/capacity requirements.
I know the great unwashed cant really tell the difference between an boeing, Airbus or the local red bus, but from a marketing perspective it is much easier showing how flash your sparkly new wonder bus is compared to the bogan mobile 787 that jetstar are using. Conversely if all three have 787's there will be a section of the market that has flown down the back of the 787 with jetstar and will think that a virgin 787 is the same (even though they may be quite different)
But I am not smart or cunning enough to work in those lofty and exalted management levels in any of the airlines