The present perfect tense ("I have never...") implies that the thing you're talking about could still happen someday. For example, you could say, "I don't know Duke. I have never met him. Could you introduce me to him?" Since Bob has died, and it's impossible for the person to ever meet him now, you would use the past simple tense instead of present perfect.

It's as Jen has explained. Note the clues, "Bob died" is a past tense time reference, while "I don't know Duke" is a present tense time reference. We use the present perfect when there is a relationship to the present, but we use the simple past where there is a specific (explicit or implicit) time in the past.