I think first it is very difficult that the price of bitcoin will reach to that high price, I think at that price no one will be able to trade bitcoin, and the second is that still majority of people do not know anything about bitcoin even they not hear the name of bitcoin so they are still using, therefore fiat is not going to worthless so easily.
In my view, there will be too many people buying Bitcoin "just for lulz" to justify it going that low. Bitcoin's wide popularity will prevent this. It is more like around $150-200 per coin being the lowest possible price for now. Cheaper than that would quickly lead to a surge in demand for bitcoins, therefore so low prices won't be sustainable.
The main reason why people trade is not because the high price or the low price, it's because the price move and they can take advantage of the price movement. It's pretty simple to understand if you are a trader especially a day trader.