Lanefan
Victoria Rules
Magic Jar, however, is doing more than just removing your spirit, it's trying to give that spirit the means to jump to someone else and take that body over, shunting that body's own spirit to one side in the process. It's a very elaborate trap, in effect.I know you said edition agnostic but, looking at the spell Magic Jar through the multiple editions: Your body becomes comatose when your soul leaves it. If the spell ends and your soul is too far away to return to your body, your body dies.
So, by that reading:
The spell allows you to stay alive even when you have no soul but you are a vegetable.
If there is no spell to preserve your body, you die. Therefore, without a soul, your body dies.
Having your original body become useless during this process seems like a suitable drawback for that specific spell to counteract the benefit of being able to take over someone else against their will, but I don't want to extrapolate from that.