Jesus Christ.... For the love of god, please get rid of this schoolboy/schoolgirl mindset! This is a worrying thing that I observe with many candidates these days. An MBB interview is not an oral exam in which you need to regurgitate a pre-conceived suite of elements! You are NOT assessed on whether you have mentioned all possible elements that could comprise an approach / an analysis/ a recommendation! You are assessed based on your capacity to come up with a sound and rigorous logic which you can follow through in order to answer a clear question. No single element that might have been "missing" will ever kick you out! It will be the totality of the discussion that you shape and drive forward which determines whether you showcase the conceptual, analytical, and communicative strength that is needed to throw the typical day-to-day consulting tasks your way and to put you in front of very demanding clients.
So don't worry too much! It is never ONE thing that determines your fate (unless you do something really crazy and improper of course).