Identity was given away after he's been killed. That is to say, he was already outed. There is no danger anymore as it's been realized and the people out for blood already got it.
If it loses that credibility, then future leakers will be dissuaded from leaking out of fear that they too will accidentally be outed in a moment of carelessness, and Wikileaks is doomed.
I don't think Assange would risk the reputation of Wikileaks like that, and think that the death of Seth Rich is unfortunately being used as means of subterfuge.