I would have stayed on this planet:
Spock wanted to stay. He said for the first time in his life he was happy.
Spock was going to stay here too:
The Next Generation would talk down about the old, outdated technology of past starships of the Original Series era, but I don’t think they encountered time travel technologies as advanced as this one.
I don’t know why that girl could not go with Spock back to the Enterprise. Why would she die? If they can go through one way and back, why wouldn’t that girl die if she went through the time portal? How would she even know that?
The Original Series characters, when they were unhibited by a drug, would express how sad and lonely they were living on the Enterprise and how they had to keep it all in.
Yet they kept choosing their career and work over love and happiness when they were offered it.
The only reason why humans have to work is because they ate the Apple in the Garden of Eden, disobeying God. Before then, they did not have to work. They just loved each other all day and all night. Their needs were all taken care of by God. Work is actually a curse, a result of the Fall.