I'd always say hi or smile. I wouldn't go out of my way to make a phone call or see the person or anything.
I wonder if the JWs are as strict about it now. I've been talking very openly to a d'ffed girl when I go to a meeting every once in awhile, nobody seems to care. Another sister always helps her with her kids.
My FIL was d'ffed, there wasn't a problem talking to him under the, "mental problems" clause.
Then, a pioneer sister came out as a lesbian and got d'ffed. I reached out to her on Facebook. She didn't want to have a friendship with me cause she felt it would cause to many problems I guess...