Is there a dashcam in the vehicle that connects to the mirror in the back? Ask me how I know this, but even though the adaptor is fantastic, taking the cover off is a certain way to ruin the plastic clips.
Parts of the car's trim falling off isn't just cosmetic, but if I were you, I'd just buy the cover and save £20. Make sure to inspect for damage the next time the cover is removed. Unless you've only had the car for a few days, I wouldn't expect Kia to cover anything if there is. Assuming it's broken, the worst-case scenario is that they'll charge you for a diagnostic.