Good question. It depends very much on the individual. What are you trying to tell that person? That he or she has dementia? That someone they love has died? You can avoid even saying anything most of the time. If you’re concerned because a person with dementia is ASKING about a deceased loved one, find out where he or she thinks their loved one is. Go with that story. “I think he’s still at work today,” you could suggest.
If someone with dementia isn’t asking, though, there’s no reason to even bring these items up.