In most cases, you will want to avoid extermination. Bats are very friendly to the outside environment, being avid insect eaters.
Some people even build bat houses outside to help with mosquito problems.
Most bat species only have one baby per year. So it takes bat populations a long time to recover from mass extermination. Contrary to popular belief, bats are not birds, but flying mammals. Most single bats found in the home are young and inexperienced bats who have strayed from their colony, and it usually happens in the late summer when the youngsters have just learned how to fly. The first rule of thumb is to try to allow the bat to escape from an open door or window.