Is it possible that Bitcoin will be regulated? And if it will be, then how would we know

I have heard stories, speculating that if someone holds 51% of the total amount of BTC they will have kind of a monopoly position and can make or break the coin alltogether. Is this true?
It is nearly impossible for anyone to "hold" 51% of all bitcoins and if they did it would mean little. It would cost 100s of trillions of dollars to buy 51%.
What you may have been referring to is a 51% attack:
https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_powerthe market cap is currently around 10 billion.. how would it cost hundreds of trilions to buy up 51% of the coins?
Is it possible that Bitcoin will be regulated? And if it will be, then how would we know

I have heard stories, speculating that if someone holds 51% of the total amount of BTC they will have kind of a monopoly position and can make or break the coin alltogether. Is this true?
No it is not possible that bitcoin will be regulated and if it was, there would be no way to know about it. It is like in China right now.
strongly disagree. look at what china has done to BTC, it's regualted them. governments can do as they please. maybe they can't completely stop BTC, but they can slow it down and ruin the price/liquidity of BTC.