User blog comment:RoyallyBella/Official Season 7 discussion blog/@comment-25830140-20160422221050/@comment-26569404-20160426101253

It wasn't Nick who decided Nabu was dead, and his death isn't just part of the Nick seasons. He was dead before they became Rainbow's partner.

In the episode before he died, the Winx received The Black Gift/Gift of Darkness. It's explicitly stated that it saves someone from death. Aisha and Nabu were the focus of the last part of that episode. Rainbow kept showing us she had a bad feeling about the meaning of the gift was.

This went on in both episodes. A few times when someone would mention death or the Black Gift, the "camera" would focus on Aisha or Nabu. Bloom also said something about the Ethereal Fairies' prophecy about someone dying possibly referring to "one of us." Nabu also said something to Aisha about "not knowing what will happen to him." All of this was foreshadowing his death.

Then it happened. He died. How do we know? Besides everything in those two episodes hinting at it, Aisha trying to use The Black Gift on him was the giveaway. It could only be used to save someone from death -- or, as the Ethereal Fairies put it, if someone is "beyond life's threshold." In other words, he had to be dead for it to work.

Everything else confirmed he's dead. Aisha dissolved his body into flowers, the Winx and the Specialists mourned him in the next episode (Bloom said something like, "I never thought it would happen to one of us"), Aisha tried to avenge him, and Morgana stated outright in the last episode he "gave his life" for the Earth Fairies. And this was in the RAI dub, not the Nick dub. It was Rainbow's own story and dialogue.

This continued into the comics as well. In #68, Roxy says Nabu "gave his life" for them. Everything involving Aisha in #97 states he's dead and that she's still mourning him. Ogron even uses her guilt against her: "He died and you did nothing to help him!" Later, she mentions she had already been trying to heal from her loss and guilt. She says Nabu "will live forever in my memories."

It's not an assumption to say he's dead. It's an assumption to say he's not dead. I don't know if Nick had something to do with why he didn't come back, but they didn't change his fate. Rainbow had already decided he was dead. The later seasons just confirmed it further.

One more thing. I loved Nabu. He was (is) one of my favorite guys ever introduced in this series, and I couldn't wait for them for he and Aisha to get married. But that's not the story Rainbow wrote for them.

I'm not ridiculing him. I'm just stating what the fanbase refuses to accept. He was a great character, but his time in the series and with Aisha is over.