That issue of being able to pickpocket Brage's corpse was resolved but @HeroicSpur brought an equally valid point that you can pickpocket his cursed sword as well. Since normally cursed items cannot be removed from inventory this should already be impossible. Of course in the quest itself though Brage gives it away, but only though a special circumstance. In any case it breaks the storyline if you can get the sword before he gives it to you.
EXPECTED: Make the cursed sword (SW2H03) in BRAGE.CRE's inventory also not pickpocketable. If it's possible to have him wield the actual cursed sword rather than the regular two-handed sword (SW2H01B), have him do that for effect. If that means he'll drop it upon death, remove the other SW2H03 that's in the inventory quickslot.