Well ideally bitcoin is a means of investment, but if you really need the money for whatever reason, you have to sell the coins to get some sort of fiat currency back.
some bitcoin holders do sell their bitcoins for fiat or exchange for alts especially after the segwit which just happened few moments ago , this will give effect to bitcoin price to fell but once that happen so many people will buy back some bitcoins just to enjoy the profit of the pump of the bitcoin price. this happens all the time