Honestly, besides people en masse across the world not having internet, the only other "killer" scenario I can think of is a massive confidence shift due to an epic bug, for example. Like ETH, despite the innovation, once people got scared their funds weren't safe, they got out. If bitcoin developed a serious exploit of this nature, we would see flight into other well established cryptos, however, not complete abandonment of the market.
Bitcoin has been there for years and there was no exploit so far. I don't think you should worry about bitcoin developing an exploit since you're not the only one that's going to be affected. I'm pretty sure if they are going to patch something or they are going to update the bitcoin network, they are going to try it out somewhere else for hundreds of times until they know that it's perfect. They don't just update things especially when it's on the Internet, when people are relying on it, and when money is involved.