JOSHUA - When is one truly an apostate in the lds church? Someone who will have a body and reign with satan as sons of perdition?

JOEL - There are various degrees of apostasy that a person can find himself in. But the kind of apostate that might get excommunicated from the Church, unless he repents, is someone who would do one or all of the following three things:

1. Repeatedly act in clear, open, and deliberate public opposition to the Church or its leaders.
2. Persist in teaching as Church doctrine information that is not Church doctrine after they have been corrected by their bishops or higher authority.
3. Continue to follow the teachings of apostate sects (such as those that advocate plural marriage) after being corrected by their bishop or higher authority.

But even most of these individuals would not fall under the category as sons of perdition. Sons of perdition include all those spirits who followed Satan in the pre-earth life and were cast out to earth without receiving bodies. They are also the few mortals who have committed the unpardonable sin against the Holy Ghost.
According to Joseph Smith the only people living on this earth who will end up as sons of perdition are those who have "received the Holy Ghost, have the heavens opened unto him, and know God, and then sin against him. After a man has sinned against the Holy Ghost, there is no repentance for him. He has got to say that the sun does not shine while he sees it; he has got to deny Jesus Christ when the heavens have been opened unto him, and to deny the plan of salvation with his eyes open to the truth of it;" (Joseph Smith, King Follett Discourse)
Few individuals have been identified as sons of perdition. For example, although Judas is often so regarded, there is a question whether he had received the Holy Ghost sufficiently to sin against it at the time of his betrayal of Christ. Only God can make a judgment on who these people are.