Creating wireless backhaul using a network of high altitude balloons is a promising solution for future high speed Internet access. Especially, it appears to be an easy and affordable solution in remote and rural areas thanks to its infrastructureless characteristics. Ease of deployment and affordability of such networks, however, comes at the price of complicated issues introduced by dynamic and complex topology of such networks. In this paper, we address the wireless backhaul reliability problem which arises due to limited control on horizontal mobility of the balloon transceivers. Despite the possibility of moving the balloons vertically, their overall trajectories are greatly dependent on the stratospheric wind which directly affects the availability of the links. In this paper, we show that using a few unmanned aerial vehicles (UAV) as relays can drastically improve the reliability of the wireless backhaul networks. We investigate the optimal paths that UAVs must follow to maximize the network reliability.