Nerys Myk wrote:
He didn't mend any timelines in ST VI. There was no alternate reality or timeline in that film. He just helped relocate some whales from the 20th Century to the 23rd Century to save the Earth from being destroyed.
He intervened in Earth's past, either completing a closed causal loop, or altering the timeline slightly and subtly changing the future
. If it is the latter, then they returned to a slightly alternate timeline (they overwrote the original). What reason do we have to suspect this happened? They didn't just locate whales. They brought bought a 20th century woman, took on a whaling vessel, stole fuel from another ship, and left behind the formula for transparent aluminum.
The sequence of time in STIV did need to be fixed, not because anyone actively changed the past through temporal hijinks, but because the human race passively stood by and allowed whales to go extinct.
And we need look no further than City on the Edge of Forever to see Spock actively working to fix temporal damage. He does so in other episodes too. He only grudgingly concedes that an F104 pilot, for example, should be returned home when he finds that his future child will be a colonist on Mars. Spock is willing to go to rather extreme measures to fix and/or preserve timelines. Edith Keeler Must Die!