As it turns out, the "see you soon" comment from Hayley Lewis is pretty much irrelevant as The Biggest Loser: Challenge Australia was filmed 9 months ago. Therefore it seems extremely likely that Loser won't be back. Season 6 contestant Nathaniel Challenor appeared on the latest MolksTVTalk podcast to discuss the season he appeared on and the future of the show. He mentions Tiff, so it's worth checking out. Apparently on Saturday mornings she rocked up to the set at 10.30am to train the contestants off camera, alongside The Commando.
Checkout these articles for more info:
TV Tonight - Ten about to cut The Biggest Loser fat
MolksTVTalk - Farewell #BiggestLoserAU