Intelligent Undead in the Forgotten Realms

[Jeff the Green]

So what happens to the souls of intelligent undead in the Forgotten Realms? I can think of two possibilities:

Their souls depart when they die, and their bodies are reanimated by evil spirits/negative energy which has the memories of their previous life, but isn't actually that person.
Their soul is trapped in their undead body and doesn't depart until they're destroyed.

I'm interested in making a misotheist character who becomes undead to avoid the Wall of the Faithless, but if option 1 is true, it's pointless. But at the same time, option 2 has problems of its own. (What if there's a long lag time between death and reanimation? What if they're destroyed, and then brought back to unlife?)

[Occasional Sage]

Szass Tam laughs at option one.

Edit: presumably all intelligent undead are treated the same. Under option one, what is the point of beginning a lich? Have hundreds or thousands of the most powerful (and therefore logically most intelligent/wisest) casters in history ALL failed to do their homework?

[hamishspence]

Liches are- some other intelligent undead (like ghosts) are- but in other cases, while the soul is present, it's "trapped in a body controlled by a malign intelligence"

Complete Divine is the main source for this.

Undead where the soul is present:
Ghosts, liches

Undead where the soul is present but the creature only retains some general memories of its former life, and the soul "is twisted toward evil if it isn't already"
Allips, bodaks.

Undead where the soul is present but "trapped in a body controlled by a malign intelligence"
A: Vampires, spectres, ghouls, ghasts, (can access memories of the deceased)
B: Shadows, wights,wraiths (can't access memories of the deceased)

Others may fall into any of these categories depending on the DM.