Another event like the K/T impactor could happen at any time. We often find objects on the way out from the earth/moon system that passed within a lunar orbit of the earth as they went by. Even if we find objects coming toward us, we really have no way to deflect them. Averaged over a huge time interval, the probability that you will be killed by an asteroid is similar to the possibility that you will be killed in a car accident. However, the probability of any such event in your lifetime is low. From the graph of megatons equivalent TNT vs. frequency, something like the K/T event happens rarely, over many million years.