This is definitely a grey area. A lot will depend on the circumstances, how the remaining Witness presents it to his BOE and their attitude toward him.
2 examples. A) The Witness works in a large factory and the d/f one is his foreman. They do not socialise and rarely speak about none work matters. That would probably be o k .
B) witness works for another one , window cleaning together all day. Either one is d/f. They spend all day on the jobs or in the van, take breaks and lunch together. He would probably have to get other employment.