Blockchain can replace a bank as long as it can be accepted by everyone in the world. But I am sure that Everyone in the world approves and likes the Blockchain system rather than using the Bank in Transaction. So in the case of Blockchain transactions it is more economical than using a Bank. Maybe someday the Blockchain will be able to replace the Bank. However, this term will be very difficult because there are so many people with different conditions and countries in the world. I think it is almost impossible to replace the bank for now.