He shouldn't have been murdered at all. One of two first acknowledge gay characters in Trek and the first thing they do is off him in a Bury Your Gays trope.
I disagree completely with this. They killed him off knowing they were going to return him later. It was built as a character/relationship arc for Culber and Stamets, and it worked out beautifully.
Culber is currently my favorite DSC character, and Wilson Cruz's performance in early S2 when they rescued him from the realm of the mycelium network is amongst his absolute best work as an actor. I think the arc brought visibility to the character (really both him and Paul), allowed the actor to shine, and cemented Culber and Stamets as one of Trek's most well-portrayed relationships across the entire franchise.
The result of that arc, and everything that came with it, elevated Culber to my most appreciated character on the show.
That felt like back-peddling at the time when the producers went on The Ready Room to reassure everyone he'd be back.
There's absolutely no evidence of that. The evidence that we have in hand is that the arc was always planned. And, even during S1 before Culber was killed, he and Stamets were described as being in a "star-crossed lovers" arc....which further supports the intent.
Just because it was emotional and it sucked when he was killed doesn't mean it was the wrong thing to do or that it shouldn't have been done. Looking back over the arc and the effect it had on the two characters, it was clearly a good development, no matter what we / I / You may have thought at the time.