Now for one of Allyn’s crackpot theories….
Spockdid stay dead after Star Trek II: The Wrath of Khan.
The post-Genesis Spock is really a clone of the original Spock, with most of the original Spock’s memories. Their brain structures are completely different; the post-Genesis Spock had his brain wired based not on the life his memories know but on the life he led on the Genesis Planet. That right there is a fundamental difference that means the post-Genesis Spock will think and act differently than the pre-Genesis Spock. It’s a problem of nature and nurture.
The post-Genesis Spock is still a Vulcan, even if his memories of Vulcan are merely intellectual and not experiential. I think it’s because of this that the Spock we see in Star Trek IV and V is so stiff and formal; he has the intellectual knowledge of the pre-Genesis Spock, but none of the emotional growth and development, and that takes him a good decade to reach. I tend to think that, had Spock not died, he wouldn’t have left Starfleet after Vulcan’s Forge. The Spock of Star Trek II was comfortable with his place in the universe, while the very different Spock of Vulcan’s Forge was not, and Starfleet was not the place for him.
As I said, it’s just a crackpot theory. I have a lot of those. 🙂