It is certain that this will not happen in the near future. Only when governments and central banks have total control over the cryptocurrencies only then. Bitcoin is designed as a decentralized currency, so any government or banking control is tackling the very essence and reason for the existence of Bitcoin.
Honestly, you idea is conflicting, you tend to say they will not happen but then stated that it will happen once the government and central banks have control over cryptocurrency.
As far as we know, cryptocurrency is either centralized or decentralized, so I believe it is very possible for the world to convert to cryptocurrency but the problem would be, there are lots of people, who are unable to use or access the technology, will be left out. The possibility of people going back to barter system will be possible for the given reason, that is if they make the paper money obsolete or not usuable.