It's a sure sign you haven't played a game for too long when you don't even know the basics for sure any more 
Anyhow, here's my problem:
I figured that having a Bakemono Sorcerer cast Twiceborn, then drown him by moving him into a see province and taking away his Ring of Water Breathing / Shambler Armour would be a good way to kill him without getting even more afflictions when he comes back as a wight.
I'm pretty sure it worked once - in the last game.
Now, I've lost 2 sorcerers (and quite some gems!), as I only get the message "XY drowned in ZZ", but no wight appears.
And before you ask, yes, I still own my capitol. In both provinces there's DOM 10. Twiceborn was successfully cast 2 turns before. And those sorcerers aren't demons/undead etc.
Where did I err ?