Electronic keys can be copied, but only if you already have an existing key. If you lose all the electronic keys then the immobilizer needs to be reprogrammed to accept a new key.
So if someone wanted to steal a car that has an immobilizer, he would need to get hold of a copy of the original key or break into the car and reprogram the immobilizer to accept a new key, (which obviously will take time).
So the usual breaking into car and hot wiring trick will not work with such a car. The thief needs to be more technically proficient.