Nabu decides to close the shadow abyss, despite Aisha's warnings. Nabu succeeds in closing the abyss, but uses up all of his energy and passes out shortly afterwards. ... After the final battle with the Black Circle Morgana tells Aisha that she will watch over him, until he wakes up.

What happened to Nabu and Aisha?

Like Bloom and Sky, they got engaged (reaffirming their parents' decision) and almost never argued. Unfortunately, the two were forced apart near the Season 4 finale, as Nabu sacrificed himself to save his friends and the Earth Fairies.

Is Dowling really dead Winx?

As it stands, Dowling does appear to be dead, and presumably will only be referenced by name in Fate: The Winx Saga season 2. However, she could potentially return in the Netflix show because of Bloom's all-powerful magic and "The Dragon Flame" that burns inside her.