I have just had a PC become inhabited by an Intellect Devourer ("ID") via the ID's Body Thief ability. I am going to let the player continue using the character, but now the player will play as the ID controlling the character's body.
First, ignoring any context. Would a message sent by the caster of a Sending spell, attempting to contact the PC, reach the ID instead?
The Sending spell description says:
You send a short message of twenty-five words or less to a creature with which you are familiar. The creature hears the message in its mind, recognizes you as the sender if it knows you, and can answer in a like manner immediately. The spell enables creatures with Intelligence scores of at least 1 to understand the meaning of your message.
You can send the message across any distance and even to other planes of existence, but if the target is on a different plane than you, there is a 5 percent chance that the message doesn’t arrive.
I'm sure we can split hairs over the semantics of which mind is now "the creature's" mind. What I'm wondering is if there are there any hard mechanics that would prevent the ID from receiving the message intended for the PC? Does the character no longer exist if their brain is gone?
Second, a the same question, with the context of the Waterdeep: Dragon Heist adventure (SPOILERS):
In Dragon Heist, Vajra Safahr is said to normally reach out to people with the Sending spell. Meloon Wardragon is a member of Force Grey and would report to Vajra. However, he is inhabited by an intellect devourer. Surely, Vajra would know something is up with Meloon if Sending exposes that he as no longer present on any plane of existence. Has she not tried to contact Meloon? Has she contacted him and reached the ID instead? Is this just poor oversight on the part of the writers?
Third, a question of how to play this as a DM running Dragon Heist (SPOILERS):
In my game, the PC in question was originally a member of the City Watch, who would have been a candidate to join the Gray Hands. Vajra would normally use Sending to do this. It will be entertaining for the player to have the ID try to infiltrate the Gray Hands as a Xanathar Guild spy. However, this will not work out if the Sending spell cannot reach the character when they appear to be alive and well. One option is that I could have Vajra just use another means of communication.
The other option is to elaborate on how Body Thief works. Narratively, I have said that the ID pulled itself and the PC's mind to a pocket of the outer planes, did some indescribable mingling with it, and reappeared in the Material Plane, inside of the PC's skull. Maybe enough of the PC's mind is there to contact and Sending just works? Or maybe Vajra chats with a non-physical mind in the outer planes (not what I want to do)?