slightly smaller odds than they are offering on Milton Keynes being the European capital of Culture 2008 (25-1)
They'll drag it out no matter what - they reserve the right to change the rules at any time, they could set a task, the winning of which would force them to take the wall down and save face (pretending that that was always in the plan) that would cheer the contestants sufficiently to keep most in. They can "break their own rules" by chucking booze into the poor house as they did when the housemates started to rebel over Sandy's last night.
They can keep putting new bodies in (maybe worth a bet there), in the end however the show will go on, but the viewers may all walk.
My money's on Alex & Milton Keynes