The consequences will only be realized if the money is needed within the next few months or even years that you can't afford for bitcoin to go down. Though I will say if anyone bought bitcoin at around $90k then that seems like a foolish idea from the start. Yes bitcoin will continue to grow in the future but you still should try to buy at the cheapest price possible. But if you already bought bitcoin at that price, prepare to ignore everything and just focus on the future when bitcoin goes up enough for you to sell it.
So, let's say you took out a loan for 5 years at 30% per annum (this is the average rate). You have bought bitcoin and you will keep it for 5 years. How much money will you use to make monthly loan payments? Let's say you have money, then why did you take out a loan? I do not know which country you are from, maybe you have loans there at 3% per annum or 0.3% per annum, then of course you can take out a loan and buy bitcoin for 5 years. There is probably no need to explain the consequences of systematic delays in loan payments. In the best case, this will lead to a restructuring of the loan, in the worst case, it will end with the sale of debt to collectors, and the consequences there can be very dangerous to health.
Well, this is my subjective opinion about borrowing money to invest in bitcoin.
You have all the data on the loan and the rest in my first message, so there's no need to imagine scenarios just to say that it's hyper-dangerous and just to write a message. If he had borrowed 50,000 euros in 2017 over 5 years, he would have earned several hundred thousand euros after tax, and that's a fact.