If you are traveling on the astral plane and some harms or even destroys your physical body, what would happen to your astral self ?

First of all, if you are planning to travel to the astral plane, you need to prepare your body to be left alone, with a protective circle around it. If, for some reason, someone found out that you had left your body and subsequently destroyed it, you’d be toast. Better to not tell anyone you plan to leave. If you have those kinds of enemies, you’d better be practicing a safe form of magick.