The truth is in the middle.
r0ach with his superbull Bitcoin to the moon as the only coin rhetoric is one extreme POV.
Anonymint with his "all your coins are crap, only mine will work" is another extreme POV.

One probable outcome in the middle - in 2020 Bitcoin will be valuable, a bunch of other cryptocoins will have half the market share, various degrees of centralization. Gold and silver will be valuable, cryptocoins will not surpass gold and silver as a store of value but will surpass them as cross border value transfer vehicles. Fiat will be less valuable than today, in various degrees depending on the country. Fiat will not disappear as long as there are bodies of people who assume governmental powers and can declare pieces of paper money. Forget one world currency and government, human nature is power struggle. A couple big secessions will happen. Taxes will be raised, inflation will be higher. A lot of this can't happen if there is a nuclear conflict, then all bets are off.