Almost every person has a Bank account rather than having a Bitcoin account.People are depended on Banks for various purposes.Banks provide them certain services such as saving accounts, mortgage, personal loans etc but Bitcoin doesnot provide them any such service. People doing jobs prefer banks over Bitcoin as they can have there salary accounts in bank .No doubt Bitcoin is the best investment asset and provides profitable investments but i dont think it can make bank dissapear. They  both will rather coexist.