IS CONSERVATION OF SPECIES ACHIEVABLE THROUGH REHABILITATION OF INJURED OR ORPHANED NATIVE ANIMALS?

With all the animals that are injured or orphaned, either due to human intervention or natural predation and sickness, there may come a time when a species population declines to the point of no longer being sustainable.  There needs to be  a large number of animals to guarantee genetic diversity for  perpetuation of a species.  Should we be keeping highly endangered animals in zoos just to preserve a species which will never become a strong population?