We can try to imagine some doomsday scenarios for Bitcoin :
Government intervention: As it spreads around the world, all governments could ban it, and that is assuming that it does not remain active on the black market.
Catastrophic coding bug: The Bitcoin Core client is one of the most active and revised open source projects. In addition, all updates are extensively tested by running them on a test network (there is a test bitcoin network, Testnet).
A better cryptocurrency appears: This is no longer possible because sidechains can be introduced anytime. In summary, side-chains are a feature of Bitcoin that allows any cryptocurrency to exist in the Bitcoin network. Thus, new cryptocurrencies can be created without devaluing or disrupting Bitcoin.
People simply lose interest: Possible, but Bitcoin has a market capitalization of $70+ billion plus all the businesses and infrastructure that have developed there. The $20+ billion growing industries do not disappear overnight.
As its network effect grows, multiple layers of applications will be built on top of the Bitcoin Blockchain, and the world will see value and trade grow like never before. Money will flow like pure information — instant, secure, unfairly cheap, open, borderless, and programmable. We will no longer be sending money, we will be streaming money.