Bitcoin can disappear?
Yes, bitcoin can disappear, but its not a central service like e.g. paypal where a single company with a single CEO can decide to close shop. Bitcoin works because many people do something for it. Some have mining equipment, some contribute code in their free time, some goods or services for bitcoin, others have servers or run full nodes from home. They all together make bitcoin work. If they all (or a larger number of them) decide to no longer care for bitcoin, it will become meaningless.
And if bitcoin is a scam, what will happen in world?
Everything about bitcoin how works is open and can be examined. If you take the time to learn more about bitcoin you will understand that bitcoin itself can not be a scam same as the internet itself cant. There are scammers that are after your bitcoin though, so be careful who you trust.
People will panic?
Many people in here will get worried if ever that happens. Through Bitcoin majority of the individuals here learn a lot of things and helped many people to their financial problems too. But atleast we don't have to worry because it will remain the existency of bitcoin as long as there is a bitcoin users like us who continually patronizing it.
I dont think so. I think if bitcoin ever disappeared its either because there is a bigger problem (e.g. no internet) or because it slowly died out.