As far as I know thertheir 'magic' is from mind and is originated from the far realmFar Realm, and has nothing to do with the weaved inWeave. In fact, that is why even Ao couldn't do much about the spell-plague. "Since the Spellplague was born from the defiling powers from the Far Realm, a plane that existed outside of Realmspace, not even Lord Ao had the power to stop it once it started.[8]" http://forgottenrealms.wikia.com/wiki/Spellplague:
Since the Spellplague was born from the defiling powers from the Far Realm, a plane that existed outside of Realmspace, not even Lord Ao had the power to stop it once it started.
And as far as I can remember, wizards and such utilize weavethe Weave while performing spells, or when they dispel something -Even Even the anti-magic zone itself is described as a zone which weavethe Weave doesn't exist in..So. So I doubt it would have any effect on a mystic from a lore perspective, as their powers drive from their minds rather than interacting with the weaveWeave.