Yes this decade would almost be the end of cash. We are surely going to see a cashless society after this decade but its not necessary that bitcoin is the answer or even crypto is the answer. You are new to the forum that is why you have such a view. As you will grow old here you will realize cryptos have endless flaws. These flaws makes it almost impossible to adopt crypto as our mainstream method for transactions.

I do not think if the fiat currency has been threatened by the existence of a new currency like bitcoin, but the currency that has been used in their country is still safe, since new digital currencies such as bitcoin are very difficult to replace the official currency, bitcoin indeed can take over for replacing the old currency like fiat and it depends on the government whether they will replace the fiat and use bitcoin as the new currency in their country or not

True! It is a threat of course however i don't think that the government will let this affect their current currency that's why they don't educate people about bitcoin to prevent it from being used by the people. It will take some time before it could replace a country's currency because not everyone is into bitcoin and not everyone is interested about cryptocurrency.

No,fiat currencies would get destroyed completely.Both fiat currency and bitcoin would co exist.Bitcoin might be used as a secondary currency.

Digital currencies are different from fiat currencies because they have their own interests, digital currencies can not replace fiat currency or vice versa and bitcoin is a technology that is highly developed up to now, while fiat currency can make payments in life daily.

Actually there is no threat in the local or current currency in bitcoins because these local currencies are used as a medium to start a investment in the company of bitcoins. 
The money is already attach in the government existence so you cannot do anything to destroy it,  instead of being threatened used this as a advantage in the competition.

Bitcoin is just a new technology invented or just a new option to make our money transaction become fast and hassle-free. Don't label it as a threat for our current fiat money. We will still be using fiat money in our life because it is still the most approved currency in the world. Bitcoin is for investment to make our fiat money grow.

I hardly think that it`s a global threat. To me, it`s just an additional tool for earning money, an alternative to an existing currency. It`s too early to think that it`s a global threat. Bankers and financial specialists used to national currency. Moreover, Bitcoin and other cryptocurrencies are too volatile and for now there`s no certain regulations of this sector.