Fortunately my country legalized Bitcoin tho is not a legal tender, now if my country never legalize Bitcoin I would still find a way to use it, since I need a currency for international cash transfer, I would find some way around to use Bitcoin, but I would not invest in it, I will immediately exchange it to local fiat in here.
You wouldn't be able to easily use or convert your Bitcoins to local fiat if the government decides to illegalize the cryptocurrency within the country and creates strict laws against those who are involved and are using the cryptocurrency within the country because you can't hide it if you are going to use your financial accounts to receive the cash that you are getting for selling your Bitcoins and authorities can easily trace where your payment is coming from and what it is for.
But this scheme to control and monitor
BTC-transactions becomes meaningless if the bitcoin is not converted into fiat. Who knows, it may happen that attempts to regulate the industry will only push people towards the massive use of currencies directly between people (P2P).
So, one can get in trouble if they use something that is banned or illegal within their country, especially if the government is strictly against its usage. Therefore, you might think that it won't be that difficult but it's not that easy as well and you can get in trouble any time if you do that and if authorities come to know about it.
So what do the authorities find out? A transaction went from address #1 to address #2, from address #2 to address #3, and so on. If there is no final conversion to fiat and all transactions occur only in the closed
BTC-system, then they will not know anything.
As a last resort, if you are afraid of problems from the government in your country, then the world map is not limited to just your country. The governments of all countries in the world will not introduce laws that discriminate against
BTC-users at once, and countries loyal to the bitcoin will still exist. At least for a while.