The exact same goes for Gold, Silver and other precious commodities. If people would stop using them for making jewelry and don't look at them as a save way to store money than the price would be a complete other. It all depends on supply and demand, and what investors think the price should be in the future. The exact same thing holds for bitcoins and other crypto currencies. As long as there are other investors who believe in their value we will have an active market to buy and sell cryptos. Just one investor will make sure that Bitcoins don't become worthless. Just imagine a new very big gold mine is being created increasing the gold supply by x2, the price would drop overnight. With bitcoins that can't happen, we can't just find a big supply nobody have heard of overnight. The limited supply of bitcoins is what makes it so valuable.