Spock should have stayed dead after TWoK.
I agree.
I like Spock and he is my most favourite character, but when someone is dead, he should stay dead. Death should be definitive, not a temporary state.
I've seen a Troi episode, where she had to pass a test. It's point was, that she should be able to send a friend to death. (Let be the fact real Geordi would do, what should be done).
Then I started to think about the end of TWOK. Everyone in the engineering knew what should be done, everybody knew what will hapen if nobody does it, but nobody did it. Like they were waiting for someone (Spock) to walk in, fix the engine and die. It quite ruins the movie for me.
I like Scotty, but his death would be right in this case. Or they should have killed Saavik instead- her character was abandoned in the fourth movie anyway. I know the backstory, but...still...
I think the idea was that as McCoy says "no human could survive that" and Spock says "as you are so fond of pointing out, I am not human."
A mere human might not have been able to survive long enough under the intense radiation in that room to fix the engines. Spock, having abilities beyond that of a human, was able to endure long enough to do what needed to be done. I guess Saavik could have done that too, but (1) she might not have had the know how, and (2) I think Spock would rather have risked himself than a much younger protege.