More questions than answers.

If we accept that the soul and spirit can be separated then what happens with someone who has withdrawn, for instance with dementia or even ptsd. Communication on any level then becomes a problem.

To help the "patient" what aspects of non-verbal communication are available to us?

Maybe: Body language, Flash cards, Habits, Time and patience.

Is there a case to add "spiritual" communication to the list?
Are the "impressions" gained via non-verbal communications in fact partly spiritual?
Is there the possibility for a man of faith use his god as an intermediary?

Perhaps more important, the patients own relationship with their god this, I feel strongly, should be nurtured. As this will sustain them when all else is gone.

The reading of the patients holy book, words of comfort or what ever is familiar.
Read aloud to the patient.

What should our expectations be?

We should not be trying to prosetylise as that makes assumptions about their desires.

A Christian communicates with the Spirit of his god via prayer and the use of what is called tongues.
That is to say he relaxes his mind and allows his spirit to do the communicating.
This is sometime specific and direct, and sometime it is in part, as though through an opaque window. Hence the use of the word "impression".

So to sit and relax and try to relate and grasp the smallest of glimmer.