Is the seller obligated to replace a defective item or refund its price at the rate he sold it for, knowing that commodity prices have increased manifold in Syria, which would cause him significant harm if he were to replace it?

If the warranty means guaranteeing the product, which is the apparent meaning, then the guarantor must fulfill what he committed to in the contract, such as repairing the device, replacing it, or other things. Repairing the defect is sufficient, and the change in currency value is of no consequence.