Re: Yesterday's Enterprise timeline
^ Not necessarily. Alt-Yar came from an alternate timeline, yes. And if she had stayed in that timeline, then she would have ceased to exist. But she did not. She was taken out of that timeline. Therefore she continued to exist.
It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shakes, the shakes become a warning. It is by caffeine alone I set my mind in motion.