[James]

They couldn't have replaced the whole house, no. We know that but the housemates couldn't be sure.

In an exercise in brinkmanship, Big Brother would have had the upperhand because they know that many of the housemates think that appearing on the show is a chance of a lifetime, and they don't want to leave.

Also, the housemates are uncertain of the public response to ones who quit or are disqualified.

And, of course, any plans that the mutineers make are known to Big Brother in advance.

I think that these reasons would have meant one warning to the rebels would be enough to get them back to their respective sides.