Oh look another thread bashing Rousey. Anyway, she's 10 times the athlete that Carano was, and while it's near impossible to stay undefeated, she's not going to rage-quit after a loss like a little Diaz. Lastly, if Tate does beat her, the trilogy fight is going to make them both very rich, so much so that any thought of quitting is out of the question.
If the UFC cuts your opponent immediately after you beat him, shouldn't that devalue your win? In essence, you've just beaten someone who isn't UFC-caliber.