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.
You are right above that. Bitcoin will become worthless unless in specific countries does not use it. But in reality many countries are open minded about the usage of bitcoin and few people does not know about it. So its impossible in bitcoin to become useless.