Some mild SPOILERS, I assume.
So, I've done his quest and I want to kill him AFTER I turn in his cloak. I've tried silencing him before he shadowdoors and I've tried paralyzing and polymorfing him, but even If I succeed, he still dissapears. Yes, he's failed his Magic Resistance and did not make a save, so TECHNICALY he can not escape, but... And of course if spell is in effect before I speak to him, I can't turn in the quest.
So, I've done his quest and I want to kill him AFTER I turn in his cloak. I've tried silencing him before he shadowdoors and I've tried paralyzing and polymorfing him, but even If I succeed, he still dissapears. Yes, he's failed his Magic Resistance and did not make a save, so TECHNICALY he can not escape, but... And of course if spell is in effect before I speak to him, I can't turn in the quest.