If it can find and approach the balloon close enough to set off a grenade, I'd probably want to target the UAV more than the balloon. If the UAV is still functional when the balloon is shredded, it could potentially just be deployed early and find a target of opportunity on the way down. Which leads to another point, if a hostile is detected inbound, they again could just launch the UAV and find something for it to go after - it wouldn't surprise me if there was a list of contingency targets along the projected route.