[RPG] What objects travel with a creature affected by Banishment

Based on the ordinary English sense of the word "native", only creatures that actually originated in a demiplane are natives of that plane. In most cases (e.g., when the demiplane spell is used), the demiplane has no inhabitants, and thus no creature is native to that demiplane. Certainly there's no reason to conclude that the caster of a spell that creates or accesses a given demiplane is a "native" of that plane.

But this is a corner case, and individual DMs might have specific ideas about how they would like it to be handled. There's no real game balance issue here.

If the spell ends, the effects still occur.

There is no evidence that the spell operates any differently if the creature affected moves to a new plane.

If the spell ends before one minute is over, the creature will return to the space it left (or the nearest unoccupied space). It would essentially teleport to where it started on the caster's plane.

If the spell goes the whole minute, the creature doesn't return to the space it left. I.e. it stays wherever it is on the plane it plane shifted to.