Scenario number one: That would be "surreal" indeed! I'd probably have a good laugh, wink at the householder, and go on to the next door. You know, "wait on Jehovah"!
Scenario number two: This one would be harder. I know a bro. from one of my old congos who has been DFed for taking a blood transfusion. I've wondered what I would do if I ran into him. I think I'd probably talk with him, perhaps in some out of the way place in order to protect us both, in case he would ever want to try and get back in. I understand his wife left him over his disagreeing with the org, so he may still want to try and save his marriage by going back. I'd not like to be DFed myself since that would put that shunning stress on those I still associate with. But I'd probably talk about the issue with him.
This is a good post!