For 4: If you destroy the evil deity, that ecological niche might be filled by some smalltime god/demon/angel.

Or by the current ruler of the really, really, nasty domain below the evil deity's domain, though he'll have to become much less evil to manage it.

I'm thinking more mystically or spiritually off-kilter. Something along the lines of, 'Evil doesn't stay vanquished forever; something always comes in to refill the power vaccuum.' But for a while, there would be a vaccuum.

Ilviak, though in may ways the most evil deity i can imagine, at least restricts his evil to a very one-on-one, intimate level. He's no megalomaniac. So my characters will be asking themselves, which is worse--Ilviak, or some upstart deity who might do massive damage to the world at large?

Chantal

Hmm. Well, there's a theological argument that you can't have good without evil, that is, you only know what is good by knowing evil. Without evil, there is no good, so I think that destroying the evil deity utterly might not be a very good idea. I imagine that chaos might result.