"What protestants call 'being saved' is from an Orthodox perspective one of the major events in that journey to God. But the mark it leaves on the soul is not indelible. It is still possible to get lost on that journey and even to go in the opposite direction by rejecting God's love."
Is there a name for that 'major event'? In your experience, have you witnessed orthodox folks who were in the process of theosis, but then outright rejected it? If so, is such a person going to be rejected at the time of judgement?
I am not aware of any specific name. From an Orthodox perspective, there may be many 'major events' on the journey to God. How about a 'sign' pointing in the right direction after being lost for some significant amount of time? Those things that point us in the right direction are very important. But the sign is not the same thing as the destination.
In your experience, have you witnessed orthodox folks who were in the process of theosis, but then outright rejected it?
I have seen people on the journey who turn away, but this may happen to any Christian in any denomination, including myself.
If so, is such a person going to be rejected at the time of judgement?
The understanding of this is somewhat different in Orthodoxy. God loves everyone equally. He loves the saint just as much as he loves the sinner, even a criminal. God rejects no one. It is we who accept or reject his love. So whether we experience God as Light and Glory or the burning fires of hell and outer darkness depends on the state of our heart. That is why it is important to stay on the journey.