There's no guarantee in this and I see you play with very very small amounts. In a loan there is always the risk of defaulting, so I will suggest to keep away from these practices, one single default in big amount can screw you for good. Bottom line, very risky method in my view.
it is not just about coins not leaving the exchanger. when you lend bitcoin on exchanger you are lending it to someone else so they can trade with it so if they lose money, it is possible that you get screwed because they can leave and never log in that account again.
there are better active platforms for lending bitcoin
Loan defaults are unheard of.. It does not happen..
If they make a bad trade they will face a margin call and a forced liquidation of their position.
I have made tens of thousands of loans on Polo and have never had a default once, not ever.. It just doesn't happen..
If they leave and never log out for one your loan term max is whatever you set it for, 2 days min, and their position will automatically renew with a new loan off the loan offers side at market..
If they just hold a margin position indefinitely it will eventually margin call based on fees (that work by time) or if the price falls..
No matter what the trader does you will get your BTC back when your loan term expires or sooner..
Out of all the thousands of loans I have made there I have never once not got my BTC back and never once not got my interest on the loan..