@Bruh : as soon as someone claims there is a consensus, which is a rather rare thing, it triggers my critical thinking.
You state, as a fact, that undead do not have souls ...
The rules do not specify if undead automatically have their soul ripped to another plane. It is not at all that black/white.
Here is an official rule quote (5e SRD) :
Undead are once-living creatures brought to a horrifying state of undeath through the practice of necromantic magic or some unholy curse. Undead include walking corpses, such as vampires and zombies, as well as bodiless spirits, such as ghosts and specters.
:
A ghost [undead] is the soul of a once-living creature, bound to haunt a specific location, creature, or object that held significance to it in its life.
Hunger for Revenge. A revenant has only one year to exact revenge. When its adversary dies, or if the revenant fails to kill its adversary before its time runs out, it crumbles to dust and its soul fades into the afterlife.
So, no, undead does not = consensus that they never have an anchored or trapped soul. It varies and DMs CAN even write-up tragic exceptions.
BUT, ANYHOW ...
I am not sure Raphael really want Astarion's soul. Astarion maybe just thinks he still has his soul (if we use your concept that he lost it).
