Sounds like if they met in the grocery, you’d be fine if they called him Mr. I disagree.
The student, no. The parents, maybe.
You do realize that semichah entails a test on certain limited portions of Shulchan Aruch, some of which aren’t very relevant to common shailos, and that the fellow may have forgotten most of what he learned.
Yes, I do. However, he doesn’t have to be a practicing rabbi to have the title, much as we still call retired doctors “Dr…”
Whether or not you should use him to answer your shailos is an entirely different question. I’m not suggesting that everyone with the title should be answering shailos, as you yourself pointed out. But we don’t revoke the title.
If a Gadol came down with dementia or Alzheimer’s or something terrible of that nature, would you no longer call him “Rav…” even though you know he can’t actually function as one anymore?
The Wolf