Defeated Rudds Labor? Very doubtful, with or without Workchoices.
Without Rudd as leader, things would still be difficult, and they might hold on with a very slim majority or hung parliament, but its unlikely as the reasons already mentioned.
It depends if Costello tries to impliment a clean slate with "the next generation" as soon as he takes the job, or whether he decides to wait until after the election to clean house (whether thats called right away or the OTL date).