Which Christian beliefs and ideas can be understood through natural theology? I think my question is best illustrated as thought experiment.

Thought Experiment

Suppose from the beginning of times God hasn't influenced development of any religion, but which I mean no prophets, no incarnations, no bible, no church. People still have spiritual experiences at the same rate as they do in our world (something like out of body experience, reincarnation memories or marian apparitions, but nothing that would allow for prophets to exist).

For a people in such world:

• Which parts of Christianity are possible and likely for them to come up with on their own?
• Which parts of Christianity are possible, but unlikely for them to come up with on their own?
• Which parts of Christianity are impossible for them to come up with on their own?

I obviously don't expect humanity in this world of full divine hiddenness to come to belief of virgin birth, for instance, or anything to do with history or mythology. By "parts of Christianity" I meant certain Christian philosophical and theological doctrines.