After seeing what the ratings are so far after just two episodes this year, I'd say its more likely the show ends (again) than the format switches.
They would have to spend quite a bit of money on promotion if the format were to change just to try to get people that have given up on the current format to possibly want to tune in again. But I think after the last four seasons (+ VIP) Seven have completely burnt that bridge and people aren't going to suddenly return to the show in droves to make it worth their while. There will still be mistrust that it will get fucked somehow. Also, there is still the lingering effect of what happened to the show on Nine that will have soured some people on the original format as well.
It doesn't have the chance of replicating whats been seen in the UK because the show (in name) hasn't been rested for five years like UK. Also they didn't completely fuck with the show to make it on a shoestring budget and try and turn it into something completely different.
Big Brother in Australia is dead.