The worldwide economy can easily affect the price of BTC because it can determine how people are either going to adopt BTC or sell it to take care of other things in their lives, but i don't think BTC can influence the worldwide economy by either making it worse or better, BTC does not have any control or influence on the worldwide economy, it is only a decentralized and censorship resistant currency that is yet to reach mass adoption.

Traditional currencies wouldn't be replaced by BTC. The current financial system has been used for a very long time now, i don't know if BTC is going to displace it, but BTC has already created an alternative for people who do not want to use the current system that is centralized and controlled by a central authority, the number of people that will choose this alternative will continue to increase and only in the future is it possible to know if it will displace the current centralized system.