You may be surprised to find that the effects of asteroids or meteors are only deterministically related to a major extinction, the Cretaceous-Palaeo extinction event. Other influences are factors that cause extinction, but not the main reason. The good news is that NASA claims to have discovered about 95% of comets and asteroids larger than 1 km in diameter. Another good news is that scientists estimate that an object needs about 100 kilometers (60 miles) wide to destroy all life. The bad news is that there are still another 5% of the situation, and we can’t do anything about the major threats to our existing technology (no, Bruce Willis can’t detonate nuclear weapons and save us). Obviously, creatures that are on zero ground due to meteor impact will die. More people will be killed by shock waves, earthquakes, tsunamis and storms. Those who survived the initial shock will find it hard to find food, because throwing debris into the atmosphere will change the climate and lead to extinction. You might want to set this to zero.