The collateral’s currency rate doesn't affect the amount of the loan buyback at the time of closing. You will receive the exact amount of collateral for the exact amount you loaned (+ accumulated APR). It doesn't matter if your collateral currency's rate goes up or down — it doesn't affect the amount you borrow. In fact, after your loan is repaid you get back the exact amount of collateral for the exact amount you borrowed before (+ accumulated APR).