RE: Theosis is an interesting idea

The LDS Church doesn't officially venture past what's been revealed - which doesn't usually get into that sort of detail. So, we are usually consigned to applying principles to current academia to make the best judgment call. For example, it's very clear "a man must be called of God, by prophecy, and by the laying on of hands by those who are in authority, to preach the Gospel and administer in the ordinances thereof." Applying this to your question about early Christian scholars, it's obvious the Church does not consider them able to preach or administer the Gospel in its fullness if they did not hold the priesthood - and I'm not aware of any document providing a chain of such authority back to Christ.

This doesn't make them apostates, however, as turning away from the gospel is not the same as not having/knowing it in the first place. Apostasy, after all, comes from within the Church, by definition.

If you want more information on the events and their causes, there are some articles from the Ensign which address the topic to a certain extent. The following are particularly useful articles I pulled from the gospel topic reference page mentioned earlier:

• ">From the Beginning - Neil A. Maxwell
• ">Apostasy, Restoration, and Lessons in Faith - Andrew C. Skinner
• ">Apostasy and Restoration - Dallin H. Oaks
• ">Restored Truth - M. Russell Ballard
• ">Whither the Early Church? - S. Kent Brown
• Early Signs of the Apostasy - Kent P. Jackson