To be honest, as controversial as the demon father plot was, that could be such a no-brainer excuse for bringing him back. The mortal part died, but being half demon or half demon-sorcerer, the immortal part still lives. Would also explain that line when Wolverine was in Hell. Jubilee said something about Kurt being a figment of Logan's imagination, like Jean, and Kurt says "But I'm the real..." then gets cut off.
"Until we meet again, Logan. Heaven, by the way? Has the greatest beer ever."
After finding out they killed him, I went back and read the issues leading up to his death and it broke my heart at how tired and burnt out he was portayed. Aholes pushed him too hard 8/
Always had a thing for blue.
There are several weird things mentioned on Azzy's wiki page. I think it boils down to editors and writers not knowing what to do with him, so therefore having no continuity with the story. In X-Infernus, Kurt tells Illyana that he's the son of a demon, and it seems like there might be a couple of other references in that direction. Then, there's the other side that says Azazel is just a really old mutant. Bah, who can say? It would still be such an easy way to bring him back.
I never really understood what the problem was. Writers didn't want to touch him during the priestly adventures, so that character progression was essentially removed during his solo run. All they had to do was build from there, yet no one did. He was a token blue splodge on the occasional panel for ages, then some numbskull started writing him as a would-be-priest again right before they killed him. Gah.
My major beef with the era/run leading up to Kurt's death was him building that church at Utopia, just in the sense that his motivation was never explained so it seemed like a huge character regression. It was sort of like they needed to re-emphasize his Catholicism to show what a moral person he is. Like, I remember at some point Cyclops saying during Fraction's run that Kurt wouldn't agree with his current direction (ie. X-Force) because of his "beliefs"; but couldn't he just disagree because he's a good person? There are plenty of other fundamental reasons (from the fact that he looks like a demon and makes up for it by being the best guy ever on downwards) for why Kurt would disagree with X-Force. I don't like the suggestion that you need to be Catholic to have morals and/or that having morals about things like killing people is a bad thing.