Check this post. It might be very difficult to make it abort with the original Korax class, but if you had a modified one with a code like this for instance:
Spoiler:It becomes easier, provided the target somehow ceases to exist during the attack sequence (think of a monster that disappears completely after death, like the Lost Soul).
Edit: Here's something to test: https://www.dropbox.com/s/x28gf610dm1ui ... g.pk3?dl=1
Load the file with Hexen and go to MAP40. Enter the first chamber where Korax* is. Summon TestDemon1. It's a friendly chaos serpent which disappears at the end of its death sequence. Let it and Korax fight each other, and if it dies and disappears while Korax is in its attack sequence, you'll get the abort.
* This is a modified Korax, made to make it easier to produce the problem.