If you borrow money at 0%, you will have to return the same amount that you borrowed. I don't know what else is here to discuss.
If you borrow money at 0% NOMINAL RATE, and deflation is 5%, it means the REAL INTEREST RATE is 5%. Not 0% as you pretended.
Okay, you borrow money at 0% interest rate (that means that you will have to return the same amount you borrowed, you name it), which is essentially the same if you just had that money. Inflation as well as deflation is 5%, your profit margin is 2%, when will you suffer losses, and when will you earn profits?