Home Planes and Death

All Gods, and many Celestials and Fiends can only be killed permanently in a specific plane of existence. If killed elsewhere, they reform in their home plane. For gods, this is their personal demiplane, whereas for lesser beings it varies tremendously.
All creatures also have a home plane. For those who can only be killed in one plane, this is nearly always their home plane, although Deva and Rakshasa are notable exceptions. A creature who is not on their home plane tends to be susceptible to certain spells and effects that can draw them back to their home plane.