Let's kick this topic,... Since nightly build r1365 it is possible to kill the avatar with the Level script. It's now possible to play each of the options listed in this topic. I've made them all: KFXLevel20.zip
If you have a new nightly, feel free to give them a try.
I hope option D becomes the standard KeeperFX scenario, as that closely matches the original game.
Options 'E', 'H' and 'I' are also very nice I think, as you'd have to kill the blue keeper but still finish the level with the Avatar. Blue needs a bit of a nerf first though, as with the new AI I think it is a bit too difficult.