As long as bitcoin and any other cryptocurrency are depending on the internet and can't be transacted without the online connection it is possible to replace dollars or any fiat all over the world, though lets not close the door that cryptocurrency may replace that money in term of exchanges as we see that the world are now open with this virtual currencies! But, weakness is still a weakness and we can't rely on it unless the issue has been solved! this is just like plastic cards we cant go out without a cash and just plastic cards to pay because we dont know when will be the system down.