Amnesia and salvation

Let’s say there is a guy and he accepts Christ and becomes a Christian. Let’s then say he experiences massive head trauma, one of the effects being severe and permanent memory loss, and another being personality change. I don’t think this is an outrageous scenario and probably has happened before.

My question is, let’s say this person does not know about Christ anymore. Let’s also say that this person is not receptive to the Gospel message. Is this person still saved? Does he need to be witnessed to? If so, then is it a different soul than the one that previously occupied the body? Is that even possible? Then where did this soul come from and where did the other soul go? What is the relationship between the soul and the body? Is it just one soul per body? If so, then what’s up with this guy? How can it be that we say he has the same soul. Or is soul separate from personality. But then how can there be such a change in personality (something that has happened) that we can still call the same soul? Or can you lose salvation only if there’s massive head trauma? Pretty problematic.