Can I send gold to someone at the other side of the globe? Can I pay my friend a tiny little bit of gold for that money I owe him for those beers he bought me last night? Can I back my gold up multiples times to protect it? That's why bitcoin is far better as a currency.
Bitcoin is more practical that's true. But for some people and in some scenarios it is less safe. For example in 2003 in there was a power outage in Northeastern and Midwestern United States and many people where out of energy for almost two days. In 1999 Southern Brazil also experienced blackout. If you have physical money you still can buy things like food and so on.
Forget blackouts, there is still a substantial section of the world population which does not even have access to the internet. Even if Bitcoin does become the global currency of choice, we need physical money to ensure that the entire population has access to a medium of exchange. I don't see fiat disappearing too soon.
There are limitations to all currencies but I don't think bitcoin will replace fiat, it's just an alternative. Obviously bitcoin will have it's drawbacks in certain situations like when you want to use it in the sticks or in the middle of the sahara desert but there are still work arounds. Anyone with a mobile phone or tablet can still send money, they'll just have to wait till they get a connection for it to be processed. You can also use paper wallets and import the money. As for blackouts its rare they happen and when they do they are resolved pretty quickly.
