Intellect devourer vs multiple heads

Question

If a creature possessed by an intellect devourer is true polymorphed into a creature with multiple heads (i.e. a hydra), what happens?

Is the intellect devourer ejected since at least one head's brain is restored? Does the intellect devourer effectively control both/all heads? Or only one?

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Other relevant answers which I'm not re-asking here:

What happens when a creature possessed by an intellect devourer is true polymorphed?

Answer 1

Nothing Changes

The Body Thief ability lists the conditions that can end it.

• If the host body is reduced to 0 hp.
• If a protection from good and evil spell is cast on the host body and drives out the devourer.
• If the host regains its brain by means of a wish spell. Not a regenerate spell, or any other means of restoring a brain. Just wish.
• If the devourer voluntarily leaves the host.

That's it. If it is not one of those conditions then the host remains possessed. Regardless of how many heads it has in ettin-chimera-hydra form. (I call it CHET-dra).

Answer 2

There's nothing in the rules to guide this choice. You would need to decide what happens. Maybe all the brains are restored and the Devourer is pushed out. Maybe the Devourer remains in control because magic. Maybe the Devourer only has partial control, like, control over one head or half the body or a 50% each turn or anything else you come up with. There can certainly be some interaction between Intellect Devourers and multiheadedness, but those interactions are entirely on the GM to come up with.