There is always that possibilty that the value of BTC can be worth zero, but this is far from happening in this reality.

There are a number of factors and indicators that drive the price of BTC in the market (e.g. demand and supply, government restrictions, creation of new cryptocurrencies, etc.) but one factor that may entirely affect its price is through government prohibition. If a country starts to prohibit its usage and almost all countries would follow that step, then expect its price to slowly become obsolete in the market.

Though that may be the case, I seriously doubt that we will arrive at that point that all countries would prohibit its usage given that there is a positive effect currently on BTC.