I don't think it is automatic that he has to quit. I know of several on this board that were df'd and still worked in the same company as some jws. In fact I know of several elders that continued a business relationship with a df'd brother.
*** w81 9/15 p. 24 par. 20 Disfellowshiping—How to View It ***Other problems arise in connection with business or employment. What if you were employed by a man who now was expelled by the congregation, or you employed a person to whom that happened? What then? If you were contractually or financially obliged to continue the business relationship for the present, you certainly would now have a different attitude toward the disfellowshiped individual. Discussion of business matters with him or contact on the job might be necessary, but spiritual discussions and social fellowship would be things of the past. In that way you could demonstrate your obedience to God and have a protective barrier for yourself. Also, this might impress on him how much his sin has cost him in various ways.—2 Cor. 6:14, 17.
*** w63 7/1 pp. 413-414 What Disfellowshiping Means ***What if a disfellowshiped person and a member of the congregation both work at the same place of secular employment? Could they have association then, since their work may require them to have communication with one another? Here again, it is a matter of recognizing the changed status of the one who is disfellowshiped. While it is permissible to converse to the extent necessary for carrying out the functions of the work, it would not be proper to associate in the sense of communicating freely, without regard for his status. Only the necessary business would be discussed, never spiritual matters or any other matter that does not come under the category of necessary business related to the secular employment. If the contact required is too frequent and intimate, the Christian could consider changing his employment so as not to violate his conscience.
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w5212/1p.735QuestionsFromReaders***Is it proper for a Christian witness of Jehovah to have business relationships with one who has been disfellowshiped?—F. G., California.The circumstances of each case might influence the answer. Generally speaking, it would be desirable for us to have no contact with disfellowshiped persons, either in business or in social and spiritual ways. If it is possible to make new business connections relative to employer, employee, the acquiring of raw materials or the performance of needed services, and so forth, it would be advisable to do so.However, if circumstances do not allow for thisas you continue to make necessary provision for yourself or family in a material way, then you may decide to continue the business contact with a disfellowshiped person. But if you deem this necessary, you must be very careful to see to it that you do not associate with the ousted one and do not discuss spiritual matters with him. Always bear in mind that our spiritual interests are of far greater concern to us than material interests, and follow closely the recommendations of the congregation regarding one who has been disfellowshiped. We safeguard not only our own personal spiritual interests by so doing, but also those of our brothers, and especially those of weaker ones or new ones who might be easily stumbled by our contact with disfellowshiped persons.