What might be a traditional Jahovah's Witness ending with fellow worshipers toward leaving their current Hall and joining a Hall in the new state?
Policywise there is nothing. Now depending on the culture of the hall, the social equity of the individual, it could be anything. Social media makes it easy to stay in touch with those you leave in one hall.
Is there a celebration or set of cultural/religious steps they might do or say at the end of their relationship at their current Hall?
Nope, nothing formal. Sometimes there will be an announcement from the stage if the person(s) were in good standing and well known. Sometimes there will be a witness party or "get-to-gether" to say goodbye, but this is all informal and varied.
What might be offered to give meaning to the end of such a relationship I have with a client who is a Witness?
The relationship is not required to end. If they move across town or within reasonable distance all relationships will likely go on. If its across the country, some contact may continue with close friends. There is no official end to relationships, their file or info travels to the next hall. Thats about it.