What happens if your body enters astral plane while under astral projection?

Question

If a creature is under astral projection and their body is transported to astral plane, for instance because they got swallowed by the 2x bag of holding combo, what will happen?

Does the astral projection instantly end?
Does the astral projection get suspended until the body gets out the plane?
Does the creature get back to their original body in the astral plane when the spell ends?

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Background:

Crawford tweets

In #DnD, the exceptional trumps the general. (No longer being a valid target trumps condition carryover.)

By entering astral plane, the creature would no longer be valid as the target of the spell (because astral projection specifically says so if the caster is on the astral plane), so I thought it will fail.

Answer 1

Read the spell failure carefully.

(the spell fails and the casting is wasted if you are already on that plane)

I think it is important to note that it does not say "Creatures on the astral plane are immune to this spell" It says the spell fails and casting is wasted if you are already on that plane.

This is important because a blanket immunity would imply an ongoing immunity, where the actual wording merely provides a fail case while the spell is being cast.

So I would say that the spell continues, with your body and astral self each located on different locations on the astral plane.

Answer 2

Your DM probably got you into this situation, so it's probably up to them to get you out of it.

This situation seems really hard to find yourself in. The particular situation you describe is almost certainly a contrived scenario - it's the kind of things players try for the very reason that no one has any idea what will happen, or it is entirely contrived for asking a question about the interaction between mechanics that realistically would never interact.

Astral projection is usually going to be used to get the entire party to the Astral Plane:

You and up to eight willing creatures within range project your astral bodies into the Astral Plane.

A situation where only a portion of the party travel via this spell is already going to be quite uncommon. A situation where half the party travels to the Astral Plane and the other half opens a bag of holding bomb on top of their friends' lifeless bodies is almost certainly not going to happen in actual play.

If this were to actually happen in game outside of the players mucking about for the sake of it, it is because the DM is using it as a plot device, and they will (should?) have thought through the mechanics of this happening.

If this does happen spontaneously, it is not at all clear from the rules how this would work, so you have to deal with whatever your DM decides in the moment.