People need loans (bank loans atm) to live. To buy a car, a house, school, etc. Our society only works with loans.
So, if bitcoin becomes HUGE, how will the bitcoin loans work?
your answer is simple, bitcoin loans would be the same way money (bank) loans are, with some sort of collateral and with big profits which you have to pay back.
right now if you want tot take a loan out from a bank you need to provide some sort of collateral or whatever you want to call it, for example when taking a loan to buy a house you sorta give your house to the bank as a guarantee that you pay them back and if not they sell your house.
so bitcoin loan should not be any different.