In the Mirror Mirror Dresdenverse I could see Harry having to kill, or set up for someone else to kill, a Red Court Susan who has become far more powerful and dangerous than Bianca ever dreamed of being. That could be a nod to both "City of Forever" and Mirror Mirror without being an exact copy of either.
Not, Mirror Mirror, because that episode had nothing to do with time travel. It was a transporter malfunction that sent Kirk and company into an alternate universe, and their counterparts into the normal universe, personality wise, each character was totally opposite. Only constant was Spock in both universes, he didn't go through the transporter, he figured out something was very wrong, and he had integrity in both universes. Our Kirk in the alternate universe suggests that after things get set straight again, that Spock needed to kill his Kirk..
Another good time travel episode was Yesterday's Enterprise, from Star Trek Next Gen. The tear in the universe is created and Picard and company investigate, in the process they see the Enterprise from twenty years or so before come through, and everything changes, the Federation is at war with the Kingons and they are losing. Also showing up as head of security is Tasha Yar, who is supposed to be dead.. Apparently there was a battle that the Enterprise was supposed to be blown up in, didn't it got sent through the tear and as a result, all of history was changed. So they figure it out, Tasha Yar realizes she is supposed to be dead, asks for and is granted a transfer to the old Enterprise, they go back through the tear, are successful and everything is restored.. One of my all time favorite episodes on a number of levels from music to acting and story...
Then instead of leaving well enough alone, they just had to screw it up.... Tasha Yar survived and married a Romulan and they had a baby girl, Denise Crosby....