Star Trek: 10 Things You Didn’t Know About The Guardian Of Forever
1. Sarek And Surak: The Untold Yesterday's Enterprise
In an early draft of the episode that would become Yesterday's Enterprise, there was no mention of Tasha Yar. In fact, it would have been a vehicle for Mark Lenard to reprise the role of Sarek, from The Original Series and films. This version of the story would have a similar overall shape to Yesteryear.
The episode would begin with a Vulcan Science team studying the Guardian of Forever, though they would inadvertently travel through time and cause the death of Surak. Surak, of course, was the Vulcan most responsible for guiding the Vulcan people through the Time Of Awakening, and without him, their society never developed into the peaceful, logical one that we knew and loved so well.
Sarek would elect to travel back through time, via the Guardian, and pretend to be Surak in the past, using his deception to set events back in their original motion. While most of this story was scrapped, it is worth noting that the idea of a major character traveling back in time was kept - only with Tasha Yar traveling back with the Enterprise-C instead.