I hope this will never happen of course, but for who have invested capitals, it may be a question someone have answered accurately to avoid an important loss.
I mean, how can you study something that hasn't happened? If you ask what will be the catalyst of the Bitcoin's fall, I understand. Bitcoin is a currency with one of the highest market capitalization compared to companies like Apple, Microsoft, Facebook, Twitter and so on. So, something expensive like this can't fall that easily.
I think that the only thing that can cause Bitcoin to dramatically drop will be Bitcoin ban worldwide and I think that the chance of it happening is slim to none.
If one or two countries bans, even if it's the USA, Bitcoin won't dramatically drop or it might drop but bounce back in a few months.