Alliance may be part owned by QF but it is not in any way a subsidiary or similar, it is a totally individual - and successful in a brutal business environment - entity who have the right to take on whomever they should choose for purposes of expansion.
There is no reason the cost effectiveness of having pilots stood down at another airline should enter their decision making.
There is no transfer of flying or similar, they would be operating as a contractor using their own staff to fulfil the agreed contract with QF.
The fact there is a "creeping assumption" from some that QF pilots will get any gigs is simply curious when there's a large supply of qualified pilots from different backgrounds that Alliance can consider, many/most whom do NOT have a guaranteed, industrially structured gig to fall back on.
As a sideline goes without saying that hopefully the current Alliance pilots will benefit from any expansion regards assignments etc but that's an internal consideration for Alliance management and its pilot group and no doubt will be a balance between fairness Vs cost effectiveness Vs practicality and whatever else you want to throw into the mix.