I live for the funny interactions between Blow and Shic and I think it would be tragic as well if Shic did kill the Demon King. We don't get a lot of background info on the characters so all we can do is speculate-- which is fun btw.
I am not familiar with all of the shows you mentioned but I have to agree that having angels would be cliche. It would be kinda late in the series to introduce angels but then if the Tower is so opposed to demons, have a giant Demon thing locked in their basement, I wouldn't put it past them to have or claim to have some kind of divine support.
Demons are also a Christian element. They are fallen angels so there is still a big possibility that we might have them in BH. Then again, there is a lot in Rood's plate right now and that new guy who got the doki doki when he sensed Rood from far away seems like the major threat right now than angels taking over.
Read more: http://blackhaze.freeforums.net/thread/61/demon-kings-cause-death#ixzz4TV4fE0BB