Yep, the Astral plane is fine for animus bodies….I mean technically the animus has some mana attached to it, holding it together…I suppose…but there is no matter on the astral plane, so no friction….
In the Abyss, you would think Animus would dissolve even quicker than on the Planes of Men. Doesn’t seem to happen. At least not to demons.
Demons regenerate very fast in the Abyss, as do humans–if they are in a more temperate region without a lot of acid in the air–this is one reason they can be tormented there for a very long time. Certainly this is true when they are brought bodily into the Abyss. Presumably a soul snatching demon would have to create them a body for the Abyss—so they can torture it
The same is true about the Planes of the Gods, although usually if you can get onto the god’s plane via the official channels (e.g. after death) a heavenly body gets created for you
I would have to say it’s part of the mystery of the Abyss…it’s a very weird place and doesn’t quite fit in well with the regular multiverse scheme.