It could happen only on the condition that no country accepts it and make it ban in their respective country. So this will discourage the people to use it and hardly anyone would be using which will make this coin worthless on a greater extent.
bitcoin can be worthless if the request for bitcoin no longer exists, or if the internet connection around the world dies and maybe if the world goes on a nuclear war that causes all internal connections in the world to be destroyed. but all these possibilities are very small to be able to happen, so bitcoin will probably remain in a very long time.