It depends on what sort of captivity. Some animals would probably be extinct or very near so if we hadn't put some of them in captivity. Of course, the reason they're almost extinct is probably our own fault, but at least some people are trying to correct the mistakes we've made as a spaecies.
Most of the times, but not always. Sometimes, natural catastrophes can also result in species extinction. The best example is that of the
Miami blue butterfly, which became extinct after the Hurricane Andrew. Several species have become extinct as a result of historical volcanic eruptions.
Also check this:
http://teacher.scholastic.com/scholasticnews/indepth/endangered_species/news/index.asp?article=turtlesandbeachmiceHurricanes Hurting Endangered SpeciesHurricanes Dennis and Katrina and two tropical storms have damaged the shrinking habitats of threatened and endangered species along the Gulf Coast. The two species most affected by the storms have been the Alabama beach mouse and sea turtles.