Wikileaks made a poll a few weeks ago asking people to vote for a way to proof that Assange is alive :

While Clinton stated "Can't we drone the guy" about Assange . His assassination is likely but In my opipinion It's going to be too obvious for the public (same case with Snowden).
I personally don't see much changing by killing him as the leaks will probably continue.
I don't think he is dead. It's just an internet rumor. If he wants popularity now, he surely won't appear so fast and easy, people are talking about him: oh my God, Assange is dead!
Maybe he is liking it and will enjoy the moment.