Wild Shape specifies that:
You automatically revert if you fall unconscious, drop to 0 hit points, or die.
When you transform, you assume the beast’s hit points and Hit Dice. When you revert to your normal form, you return to the number of hit points you had before you transformed. However, if you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form. For example, if you take 10 damage in animal form and have only 1 hit point left, you revert and take 9 damage. As long as the excess damage doesn’t reduce your normal form to 0 hit points, you aren’t knocked unconscious.
Blackrazor specifies that:
Whenever you use it to reduce a creature to 0 hit points, the sword slays the creature and devours its soul, unless it is a construct or an undead. A creature whose soul has been devoured by Blackrazor can be restored to life only by a wish spell.
Blackrazor states that it slays the creature when it reduces it to 0 hit points, which is similar to the wording Disintegrate used to have (and old Disintegrate used to kill Wild shapers): "If this damage reduces the target to 0 hit points, it is disintegrated" vs. "Whenever you use it to reduce a creature to 0 hit points, the sword slays the creature and devours its soul". This hasn't gotten errata'd though, so am I correct by RAW in assuming that Blackrazor still sucks the soul if the animal form gets dropped to 0 HP?