The impact that killed the dinosaurs was a almost 6-mile-wide asteroid striking the Earth.An impact like that on a world smaller than us would most likely end all life on that planet or moon.The para-teraformed moons are in even more danger that the moons that are terraformed.If the domes break then the atmosphere would vanish though depending on the size of the hole it could be patched before much leaks out. To prevent this from happening we need to somehow reverse the asteriod. or maybe we could fling it using gravity.